Easy answer is "not really". Longer answer with some work involved could be "yes sort of".
Black Crusade reworked some of the balance of the game system. So making a Deathwatch character for it would be similar to making one for a Rogue Trader game in that you can do it but you will either have to scale the SM back or push everyone else up. But with Black Crusade you will have to convert a few things over too as well as scale around him. It can be done and there is no real, "Do this fist, then do this instead of this" sort of answer, you will have to take it all on a case by case bases to keep balance.
The other way to go about it would be to just do it and throw him in whole sale. It can work, your Deathwatch character will just be stronger than the others. This can be ok depending on the group and the player. I, for instance, know one of my players would be able to run something like that because he would intentionally hinder himself to keep it fun, but it could quickly get out of hand if that one character is dominating everything and over everyone...
Anway just my thoughts on it.
