Ron send mostly of his own goblins in there, that has around 3,000 troops in total, with some special troops, they were Boar Riders, they has 200 member's.
Ron didn't send them for 3 reasons. First, it was not nessary, adding them will be overkill, he was glad that he didn't do that, or he will not be able to see such amazing battle, where the battle was some what balance.
Second, it would have disrupt the flow of the main arms, Slimes and Rats have a good strategy, as they each compliment each other, and also Ron developed this strategy perviously, so adding extra troops in the mixed was not ideal. This also would have disrupt the battle rhythms. He would have called them if it was nessary.
Third, it makes him feel bad, having them fight each other, as his goblins were weak compere to the goblin tribe. As they would not bring any significant changes in the overall battle.
