I have looked for an answer, but failed. I hope someone here can find it. It seems to me that ordination to the episcopacy would indicate that the man is a diocesan priest. This would be specifically true of diocesan bishops (ordinaries) but also of auxiliaries who are canonically subject to the diocesan bishop in the same way as the diocesan priests are. Every bishop who is not a diocesan bishop (auxiliaries, Vatican officials, etc.) holds a title to a (usually) suppressed diocese, a symbolic nod to the theological proposition that a bishop, by definition, is pastor to a particular church.  I think that when the pope nominates a religious as bishop, the religious superior must release him from his vows to the community (especially if the vows include stability). Some bishops from religious communities return to those communities when they retire; some don't. Most continue to identify with their communities by wearing their habits, using the community's identifying initials, etc.