Well, at least in the 18th century, and for higher ranks, the opportunity to diddle the payout to the men, fudge the rations, carry dead bodies on the roster, etc., would allow quite a comfortable living. I'm guessing the Duke of York put an end to the worst of that, though. I think, though, it was more or less tacitly assumed an officer had other sources of income, although since it was the route for younger sons, there might not have been very much on the side. All the more reason why officers promoted from the ranks tended not to fare very well in their new status.
The army was always jealous of the navy's right to prize money, since the equivalent on land had gradually died away since the 15th and 16th centuries; officers and men had few legitimate opportunities to acquire wealth that way any longer.
YHOS,
Snarkhunter