Good question!
Positive and supportive posting is what PC is all about, so yes, one can post something in that regard. Don't forget we have the Kudos and Affirmations forum as well when we want to recognize a member in a positive way!
Discussion of a member that goes into their personal struggles may not be particularly appropriate if posting becomes unsupportive. By that I mean if you post specific issues that the member may be dealing with or if you and that member have had a falling out would not be appropriate. Apologies or trying to work through a fall out would best be done privately via pm and not on the forums.
I hope that clears it up for you.