Metaphysically-speaking, those pronouns would be fine because God is essentially genderless since He is spirit. But, quite obviously He refers to Himself as "He" so the point is moot. Further pushback is refuted by the simple fact that pure act is masculine because it is non-receptive, while creatures are receptive, so a male pronoun would still be most appropriate in reference to God.
So now this heretic is an idiot on two points of theology.
"They" might in fact be rather appropriate, but only because the plural is a royal form, and the singular name of the One True God in the Old Testament Hebrew was in fact a plural ... hinting to us about the Three Persons of the Holy Trinity before they were formally revealed. Nevertheless, this priest's agenda is to condone gender-neutrality. Certainly, God is above gender, in that He has all the perfections of both the masculine and the feminine, but the term Father is not merely a gender term. It's a term of relationship as well. Fathers are the heads of their families, and that is why Our Lord calls Him Our Father. It is in fact the erosion of the notion that men are the heads of societies that has led to this point. If there's no distinction (other than gender) between a father and a mother, then this might even make some sense. But there is. In fact, even Wojtyla correctly taught (in broken clock fashion) that there are ONTOLOGICAL differences (and not merely physical) between men and women. For Our Lord to have called God "Mother" would have put him in a subordinate position to some unknown and unspecified head.
In other words, it's this notion of gender equality that does not acknowledge any essential and ontological differences between men and women (reducing them to mere physical accidents) that has led to this point.