Hearthpwn

Do you have the cards to test if this even works as you expect it? I don't, but I assume the triggers work similar to the Call to Arms and Knife Juggler interaction, where Knife Juggler would only trigger for each minions summed after him. So, if Master Oakheart recruits them in the sequence given on his card text it would not trigger Spiritsinger Umbra, thus foiling your combo.