Check the CSS file
The easiest way to tell if an icon set is going to be compatible with Divi Upload Icons is to open up the CSS file that came with the icon set and check the code.
What you’re looking for is code that looks similar to the following:
If the CSS stylesheet contains a bunch of statements that look similar to that, that is, a class name followed by a psuedo element (like :before and :after) and contains the property ‘content:’ followed by a unicode (in the example here, it’s \F003), your icon set will most likely work with Divi Upload Icons.
The only way to be sure is to upload it and find out, though!