Short answer is 'no', you can't give training in the US on a foreign instructor licence. You must have the FAA Instructor rating. This is shown in FAR 61.3(d)(2), 61. 41 and 61.181
Although they cannot be signed off for exams or tests (only an FAA instructor can do this), a pilot in the US can count training done in another country towards the requirements, if the instructor is from a ICAO contracting state.
You can find these references at
http://www.airweb.faa.gov/Regulatory...ary/rgFAR.nsf/ and go and look in Current FARS
Instructor Pay rates range from $15-25 per hour. Not much compared with the UK (especially with the dollar-pound/Euro rates at the moment.)
As far as ATPL, I can't really answer this...I am not the one doing hiring. However, I have stayed away from the 'FROZEN-ATPL' for the reason that if I don't manage to get the IR and Multi-time in 3 years, then I'm stuffed!
I will do that when I know I'm on the IR and Multitime path.
cl12pv2s