Define “participate” in this situation. The answer depends upon who you ask! It also depends upon the actual M(m)ass and priest. Is the priest actually a priest? Did the person receive Communion (or just a piece of flat bread?) Were the novus ordo rubrics followed? Are they valid, even if the most conservative and perhaps in Latin?
What about the person who attended? What does he or she understand of the Faith? Did he participate despite serious doubts out of human respect? Did his participation give scandal?
I don’t think this question can be answered until the Church returns to Her right mind!
For what it’s worth, I treat going to a novus ordo as I’d treat attending a Protestant service for reasons of avoiding scandal, professional obligation, etc. If no scandal is given to those in Tradition, I’ll attend, but refrain from direct participation. Anything clearly against the traditional Faith or morals, I shun entirely. In other matters, ie. social small talk afterwards, etc., I let charity prevail.