As long as it's not a thinly-veiled effort to attack the IRs. Having an elite army is not the same as excluding less active players from battle, though both can be done in one move. Hence why elite armies in themselves are fine, but they don't give you the right to exclude the others from war due to their activity levels.
There is no IR that covers this. I can't tell you what units to command sure, but as a Lord no IR compels me to appoint you to an army.
