She's not an Imperial legionnaire if I remember, but a soldier of the EEC, which is an independent company
Pretty much one and the same. Like those of the East India Company of the British Empire. They all served Britain in the end.
And besides, it's one of the Empires biggest earners. Ulfric would be doing his cause some good I'd assume if he just evicted them, unless it's a case of Napoleonic Hypocrisy.