Yes, there are. You have to check what armies are allies to you. You can include allied units in your army. Only every 4th (inluding allied units) can by an ally. Also - depending on Game Type - there is point limit to allies. In Vanguard type games (1000) you can spend up to 200 for allies, while in Batlehost type games (2000) it can go up to 400. Allied battleline units do not count towards battleline units in army. Allied units do count towards max. number of Behemoths, Leaders, Artillery etc. Allied leader cannot be a General in your army*. Allied model do not benefit from yours army allegiance and cannot use abilities of you allegiance [so no artifacts for allied leader]. If allied units are part of a battalion, and are from the same Grand Allegiance, they do not count toward points spend for allies and for the rule of "every forth unit".
If you have any further question - please feel free to ask.
P.S. Sorry for bad english
*harbingers can be Generals, and can be your allied unit - even if not listed. For Ironjawz it would be Fungoid.