Employer stamps are fine As far as I have been told
The American FAA, and all American employers, do NOT stamp any licenses or logbooks. They don't even know what that means. Some airlines/CAA organizations do not realize that "stamping" is not done at all in the US.
I got my FAA license validated in the way posted above, and I got documentation (signed letters, or official forms), from my past aviation organizations to verify my flight time and experience.
cliff
NRT