In order to be allowed onto the flight deck to perform your duties you must be wearing a FR uniform, if you don't you don't fly.
I would imagin the above to be pretty vital to the business, as with licence costs, medical, time spent away from home base and travel costs getting from home base to temporary base, expenses etc.
The way I see it is if you cannot do your job without it, then you can claim it.
Cannot start without a Typerating, would not be incurring the cost if you didn't start with the company, tax deductable.
Don't see the issue with paying tax in lump sums, after all it is sitting acruing interest in the bank until the tax man arrives!!
may be wrong
Nick