I use a Wii controller with the classic Wii controller attached to play Shadowgun, you also need to download "WIImote controller" from the android market (its free), open the battery compartment on your wii controller (your looking for the red sync button), open the app and click "init and connect" and click the red sync button the program is now synced up with the controller.
Next go to settings, language and input, current input method & change to "WiicontrollerIME" (when you need to go back to onscreen keyboard input, go back here and change it to keyboard)
On the same menu click "Configure input method", scroll down to WiicontrollerIME and click "Settings", then click "Mapping options", then click "1st Controller mappings", scroll down to the "1st classic controller", below are the keys I used for Shadowgun, click each button you'll be using on the controller then click the letter I have showing what the action will do in the Shadowgun game.
7-Reload
D-Pad Center-Fire
D-Pad Up, Left, Down, Right-Analog 1
A-Shotgun
D-SMG
I-Analog 2 Up
J-Analog 2 Left
K-Analog 2 Down
L-Analog 2 Right
S-Rocket Launcher
W-Grenade Launcher
Back-Pause Game
I used the following for my setup:
x = number 7
y = D
a = A
b = Dpad center
start = Back
left stick up = Dpad up
left stick down = Dpad down
left stick left = Dpad left
left stick right = Dpad right
right stick up = I
right stick down = K
right stick left = J
right stick right = L
L = S
R = W
Shadowgunning on a 32" HDTV, yeah baby!