Lot of issues with that, but it would be possible. I am not to educated on the cool hoods, but I would imagine the heat will need to go somewhere (ducted). I grow (veg only) in a closet not unlike yours and without external venting. I use a 250w MH and CFL's - and the temps stay around 75 with a little 8" fan and the doors cracked 1/4"-1/2".

Problems I see:
1. The mold (as you stated)
2. Smell when flowering (it will be so bad that you will taste it)
3. 400w in the narrow space might not be that effective on a cost analysis( Use a track maybe)