Thug, have you met Billy Burke? Are you considering his school for enrollment, or what? What made you suspicious of his claims? Also, why are you interested in Michael Echanis? Echanis' death under mysterious circumstances in Nicaragua makes it kind of hard to verify if someone trained with him. Burke doesn't claim he met him in the service, so it is possible he trained with him when Echanis was a mercenary.
If you are considering training under Burke, why not just call him up and ask him for military references?
Now, one thing that does make me suspicious of his claims is that Echanis was a buddy of none other than John M. La Tourrette, a bullshitter who claims four 10th degree black belts, and the subject of another bs thread that you can locate on this site (just do a search). The fact that Echanis was at one point involved with La Tourrette, and is now being used as a reference by Burke, makes Burke "look" suspicious. But you're going to need a hell of a lot more facts here. You need to do more research.