I know it's in the rule book but don't have one and htis is easier than looking it up anyways. Anyways, here's my question:

General Secura gives Order 66 followers an extra attack, Rex gives them greater mobile. Are the two stackable, if you will, for example can a SEV have double attack with greater mobile now?

Yes. Greater Mobile Attack just requires that you make all your attacks at the same time. You can't attack move then attack.

No offense meant, but in the future. Don't be lazy.

Seriously though, sometimes you can find answers like this in our Archives as well, if you don't have a rule-book handy.