As for "revelations" to non-Catholics, God obviously CAN do as He pleases, for purposes known only to Him, usually with a view toward granting some kind of actual grace toward their conversion.
Generally speaking, however, 99% of all claims to private revelations are fraudulent, being of human origin, while 90% of the remaining 1% are of diabolical origin. Obviously I don't have actual stats, so this is just my generalization. Human fraud can be either deliberate, conscious, and intentional (with a view toward some gain -- fame or fortune, the respect and admiration of others) or else an active imagination combined with an inability to discern between the workings of their own imagination and reality. Some people with active imaginations ... it's little wonder that the vast majority of "private revelation" claims come from women ... decide that what was really the product of their own imagination actually came from God. St. Theresa of Avila, when she was told of a nun having "visions" would order that more meat be given in her diet. True "private revelations" are very rare.
God avoids granting private revelations in a way that might give the impression that He approves of something He does not. Thus, He does not grant them to non-Catholics, as this might lead to the impression that God favors and approves of non-Catholics and works through them. God might work IN them, toward their conversion, but He will not work THROUGH them.
Unfortunately, even some of the Traditional Bishops have succuмbed to excessive credulity with regard to private revelations, Bishop Williamson to "Dawn Marie," Valtorta, Akita, and Garabandal, and Bishop Fellay (and quite a number of priests) to this Rossiniere (Cornaz). Archbishop Thuc fell for Palmar de Troya (led there by a seminary professor from Econe).
But our attitude, following the mind of the Church, must be that of extreme skepticism. Whenever presented with claims of private revelations or miracles, the Church's default attitude is that they are not genuine, and the VERY FIRST criterion the Church applies is that of sound doctrine If something runs afoul of Catholic doctrine, it is immediately rejected without any further consideration. If the doctrine is sound, then the investigation proceeds to evaluationg the virtues of the visionary (whether he be Catholic, demonstrate solid virtue, especially with regard to obedience). Church will never even consider revelations to a non-Catholic, as those are non-starters right out of the gate.
So we too apply Catholic theology to test these private revelations and never modify Catholic theology based on the claims of private revelations or based on miracles. Thus we have Bishop Williamson growing increasingly "soft" regarding the New Mass, as "undisputed Eucharistic miracles" ("just look them up on the internet", he says

), at first asserting these prove validity and then that the NOM cannot be "completely" condemned.
Nonsense. Satan can simulate just about any "miracle" with very little exertion on his part. So the ones that cannot be written off as either due to natural causes (including human fraud), for him these cannot be "disputed" ... as of the devil cannot also simulate "miracles". It would require little effort on the devil's part to introduce some blood or human heart muscle onto the scene, replacing some of the bread with flesh and blood. We know that the New Mass is a bastard rite that displeases God and harms souls. God would never work a "miracle" that might possibly give the impression that the New Mass pleases Him ... which is precisel how most would take such "miracles". Well, if God deigned to work a "miracle" in the NOM, it must be valid AND it must be OK for me to go to the NOM, since it can't displease Him too much if I go. Why would God encourage people to assist that this offensive Protestantized bastard rite of "Mass" that has blasphemously replaced the Catholic Offertory with тαℓмυdic filth?
To take this one step farther, however, these "miracles", if not due to human fraud but rather to diabolical activity, would actually desmosnstrate the INVALIDITY of the NOM, because God would not allow the devil to tamper with the actual valid Blessed Sacrament.
So, no, God does not grant private revelations to non-Catholics except with a view to their conversion. You'll see that many / most of their purported "messages" from God actually confirm their Protestant views ... and therefore must be rejected out of hand as either made-up or diabolical. God would never approve or or condone Protestantism. As I said, we apply Catholic doctrine to test revelations (those alleged by non-Catholics are to be rejected out of hand). So we reject Prot revelations rather than to start questioning whether Protestantism is REALLY wrong and offensive to God ... and questioning EENS dogma.
Those who easily fall prey to private revelations, miracles, and other such allegedly-preternatural phenomena demonstrate a weakness of faith and a lack of conviction in their principles. We don't need this garbage. We have our faith and the teaching of the Church. We don't need some "revelation" to a Traditional Catholic, like a Dawn Marie or Rossiniere, to demonstrate that Traditional Catholicism pleases God and is the right path through this crisis, and that the NOM is offensive to God.