Is it good practice to share pre-print of PhD thesis?
I think that question can only be answered by your University and your advisor. It is conceivable that they have some rule prohibiting it. I think that is unlikely, but you should learn first. Even if it is not forbidden, your advisor can give you feedback on whether it is advisable in your case. 

If you were submitting to a formal publication, on the other hand, their rules might also be important to consider.