Modeling portfolios and Model Mayhem
For the most part, the answer is no. Being on those websites is the mark of an amateur. While there are a few professional models that use these websites for social purposes, most refrain from participating on them. And most agencies dislike their talent being on them.
There are many reasons why, but you need not look much beyond what they are: amateur modeling websites. Most the talent that considers themselves professional on these websites are those who consider amateur photographers their clients.
Modeling agencies dislike their talent from being on because it speaks poorly of their talent if clients see them there. Amateur modeling websites are largely for hobbyists.
There are many places you can post images from your modeling portfolio in case someone asks you for a link. They do not need to be “modeling” related.