In this case, "reasonable accommodation" is simply butting out of his off the field use of pot.
It's not accommodating someone in a wheelchair to give him ankle weights to build up leg his strength. Accommodation implies accepting and working around the disability.
And what's there to work around? As far as showing up for work and being prepared, the ban is the limitation, not the pot. His rehab stints were about Gregory accommodating the NFL's intrusive policy, not the other way around.
I think that is completely wrong because I don't think a federal law like the ADA would require employers to ignore federal law regarding drug use. A wheelchair doesn't violate federal law - possessing and using pot does. And let's not act like the NFL is unique in testing for pot. All sorts of employers do, and people can be fired for it.
One possible argument might be if Gregory's doctors prescribed medical marijuana, but again, that might be acceptable under the laws of some states, but it is not acceptable under federal law. So, again, I can't imagine the ADA would require an employer to ignore federal law.
Don't get me wrong. I personally don't give one hoot whether Gregory or anyone else uses pot as long as they aren't driving under the influence. And perhaps the NFL's testing is intrusive, but it happens all over the country, and employers all over the country can fire employees for using it. In the end, whether you and I like it or not, if an employer has the right to test, and they choose to do so, the employee has to live with it or risk losing his job. And where else besides the NFL can an employee fail drug tests 6-7 times and still get a chance to come back and work for the same employer?