Yes, I think Texas A&M was one of the schools that encouraged it. As the husband of a dental student you better believe I was involved in every step of the process, including the interview day. It's not just her moving to a new city and taking on a huge amount of debt, stress, etc, we both are. So to have family, especially family that close, involved seems perfectly reasonable to me.
That said, notice I said "interview day", I do think it would be a tad awkward to have a family member sit with you in the waiting areas for the actual interview part. At Texas A&M, since they encouraged family involvement, I actually walked to the school with her that morning and almost all the way to the interview area, told her good luck, and then proceeded to get lost in that cavernous maze trying to find my way out... I spent the rest of the day exploring the surrounding area.
Same at the other Texas schools, but I just dropped her off since they didn't have the "bring your fam!" stuff. I did scope out the areas though. It can be a pretty big decision for people close to the applicant.
She now attends that maze school...