How legitimate is EPGY for colleges?

It’s really your call what you end up doing. All I’m saying is that to this: “was unable to take AP Physics C at our school so I found an online version” EPGY physics is not an exact online version. An online version is an accredited AP online class such as John Hopkins AP Physics (albeit they don’t have C)

The difference is in how the content is structured, and how your school and college admissions look at it. Don’t try to do it for AP Credit, because “This course can help students prepare for the Physics C: Mechanics Advanced Placement (AP) exam.” does not mean that it’s accredited by the College Board, so you’re not gonna get AP weight if you choose to take it (and why would you want to if you don’t get AP credit).