It's totally fine! I personally haven't noticed any difference in stress on my body, (but I'm also only 18; plenty of time left for my joints to start protesting) but I've heard that riding aside is GREAT for people who have difficulty riding astride, for whatever reason. You're very, very secure in the saddle, and in an emergency situation, if you clamp down your thighs on the bars, you are not going ANYWHERE.
The saddle I ride in is very comfy, and both I and my horse prefer it to riding astride now :)
TL;DR: I don't know for sure, but have heard it can help people with bad legs, so can only assume that could extend towards hips as well.