A lot of info came out about VADA during the whole Hendricks vs. GSP WADA vs. VADA saga and it was made pretty clear that VADA and WADA are ahead of USADA, but USADA uses WADAs banned substances list.
I think the thing with all of this is that it's really all about the appearance of being tough on PEDs. So I think that the reality is that the UFC wants to look like they're cracking down on PEDs and if they catch some cheaters here and there then that's great.
The reality is that if someone really wants to cheat, they're going to find a way to cheat. It's gonna happen somehow. So all the UFC can really do is look like they're trying, which they're doing. Theres no reason for them to spend way more money to use VADA when it won't make much, if any, of a difference.