First, the license for the individual pieces of work. There's a generic "wiki" license on the site which essentially says they own everything save for "fair use", which muddy as heck.
What I'm talking about here is not the use of any particular likeness, but of the rendition of that license. Since you have an SVG file, that, in itself, is licensable content - like any software.
Next, is the actual use of the likenesses. If I get a Twitter logo from here, can I use it? That's more a trademark issue and probably falls under that umbrella.
But you can see how you may be allowed to use a likeness because of trademark policy, but not allowed to use THESE, SPECIFIC incarnations of a likeness.
Vice a versa, these folks may well let you use their likenesses, but the trademark issues prohibit it.
So, anyway, in the end, there's not a single license involved here, me thinks, but potentially two.
