Yes you can.
Minor rules separate the system but are 100% compatible for gaming.
Warmachine, warcasters spend focus and get there full focus every round
Hordes, warlocks spend fury (same as focus) but you only get fury by leaching fury from your own warbeasts. You force the beasts and place markers on them, when your warlock leaches if fury markers are left on any warbeasts you have to take threshold checks, if you fail the beast goes nuts and may even attack your own troops.
Warmachine is a reliable source of magic, where Hordes you have to make sure you look ahead a little to get your spells.
Why do I play Hordes instead of Warmachine?
With Mark 1 Warmachine Warjacks (the big steam powered robots) I want to use lots of Warjack and the game is more Troop machine due to troops being more powerful (game wise) then warjacks.
Hordes forces you to take beasts as it's your power source for your warlock, so I wanted the cool big toy's.
January 2010 Mark 2 Warmachine will be released and Warjacks will once again be worth taking.
See in the pic below,
The largest beast as 2 blue tokens on it? The warlock forced it to use 2 fury. See the square piece of paper in front of them? That says rage, the Dire Troll Mauler has an animus (type of spell with a 6 inch range) that increases the targets strength by 3.
See the warbeast with a giant spear in his hand? that is a Troll impaler, he has 3 fury tokens on him, he used his animus, called far strike the piece of paper near him say's far strike, increases your range by 4 inches and then boosted the damage roll for the third token.
See the 3 tokens behind the model charing a large stone on his shoulders?
That is a Kriel stone bearer unit, the stone holds fury (so my warlock can dump fury into it and they use it or the warlock and use it later).
They spend one fury and create a force field that helps out everyone, but the range varies with the number of fury points in it. 3 tokens is a range of 7 inches.
See the unpainted model between the impaler and the mauler?
That is my warlock he used some of his fury to activate the animus on the impaler and gave himself far strike, he throws his axe.
The fog cloud you see move around is from 2 small little goblins that carry a smoke screen maker, the best models in the game!!!