Just use miners to make up for your lack of mobility. No cannon does free up lots of lovely special slots.
I agree. the problem with any dwarf army is that its very slow and unmobile force. it takes half the game to get to the other side. i myself am actually thinking about doing one. the black powder idea isn't bad. But i would highly encourage you to use crossbowmen and bolt throwers as well. the fact that you can use 2 of them as one choice is awesome. miners i think, are a must. very mobile and really annoy the enemy
good luck with the dwarf army man