I have very mixed experiences with upwork, no good ones for SEO, some lovely ones for a marketing adviser and photoshopping of images, but terrible for website design. Am in the middle of a dispute now, the designer was supposed to do design templates for 3 specific pages, and the layouts, looked great. However his integrating was and still is a mess, affecting text and layout on all the pages, to the extent, that I am now having to spend hours undoing and re-doing all the work. And the upwork view..." it appears that no clear violation of our terms has been made"
So sure, use them, but you are entirely alone if it goes wrong.