I'm not sure if it's supported by default. I will say before I offer my (temporary) solution that although the game does feel like a console port I have played it on the original Xbox and to be honest, the mouse and keyboard feels much better. I'm not here to judge your opinions though so here is a solution that may be suitable for you.
You can download Pinnacle Game Profiler (Only a 30 day trial unfortunately, there are probably free alternatives that you can find but I tend to stick with Pinnacle) and run it in the background while you play Enclave.
http://pinnaclegameprofiler.com/downloads/30-day-trial You can create your own profile, but the developers of Pinnacle have released an official profile for the game which can be found here.
http://pinnaclegameprofiler.com/forum/showthread.php?t=1000&highlight=Enclave Just download the profile and load up in Pinnacle and then have it running in the background while you play. Everything should work then.
Hope this works out for you.
Edit: Although I have tested Pinnacle several times with games such as Oblivion and Minecraft, I haven't tested it for Enclave. I will do so now and get back to you with the results.
Edit 2: Forgot that you need to register to download from the Pinnacle forums, here is a mirror for you in case you don't want to.
http://www.sendspace.com/file/8ogyod Edit 3: Everything works fine. Only problem is if you are like me and launch all of your GOG games through steam so you can talk to your friends, forget about it. As far as I know you have to launch the game through the Pinnacle interface or else the profile won't work. In my personal opinion the keyboard and mouse works better in game, but here are the controls.
A = Jump
B = Health Potions
X = First Person
Y = Unknown
Click down right analogue stick = Crouch
Click down left analogue stick = Nothing/Unknown
D-Pad = Nothing
Right Trigger = Mouse 1/Attack
Left Trigger = Mouse 2/Block/Activate
LB = Switch between off-hand and torch.
RB = Switch main weapon.
Bear in mind that if you bought the game from gog, once you activate the profile, you will need to edit it and change the install directory to where you installed the game.
Edit 5: Cor blimey. Lots of edits! Anyway, I've just figured out that if you want to launch the .exe through Steam you can Edit the profile and check "Do not start the executable file when this profile is launched." This will allow you to activate a profile and then launch the game however you choose. Sorry for the many edits but I'm just rediscovering Pinnacle for myself and these features are quite new to me.
