The support mainly deals with templates. PIX OS 7.0 was not fully tested in terms of what CLI commands will be supported. Provided you push commands down that are understood, you should be able to configure a PIX running 7.x.
As for why the PIX 535 is not supported, I see no reason for that. It is managed the same as the other PIX models. I believe this is a legacy item carried over from RME 3.5, and Netconfig with the PIX 535 should work fine.