From: The Imperial Palace.
Hmm. On the one hand, in this game, units can and do gain a little experience if they are successful in battle. On the other hand, there's often incentive not to use the Minors in any dangerous engagement, as Minor casualties can hurt your political standing with their governments, which in turn leads to fewer replacements and reinforcements. If casualties get really bad, or if the war goes very badly, the Minor governments will abandon you altogether.
Another interesting facet of the Minors in this game is that you have to keep a majority under their own national command. In some circumstances, you even have to ensure they have their own national Army command. Very interesting set of rules.
I tend to use the Minors in defensive and support roles, asking them to hold parts of the line while German troops do the encircling and attacking. But inevitably, sometimes you do have to call on the Minors to fight. And of course, the Sovs have some say in the matter; they may pick on the Minors, as they did historically.
Hope this helps some.