Just to follow up on Oyster's point. Joining these programs is optional and up to the individual. Would I be acting unethically if I didn't personally join every program associated with each and every hotel and airline that I used and then attempt to maximise it's value to my employer? If that were the case, I should be able to expense a payment to FT as well. And it would be required reading!

Larger companies negotiate their own FF agreements in the form of structured discounts based on volume. If it was my own, small start-up, I'd definitely use my personal miles for business purposes. But I'd have to carefully consider whether I'd ask an employee to give up points unless it was possible to compensate for or manage travel within normal business hours.