The engine needs to support explicit vertex normals for that to work in game. Guess you should ask whoever does that engine if it works. The only engine I know it works in is UDK.
That's basically how I do my branches for leaves too. I paint the branch using my Wacom, use that as a mask over the bark texture that I use on the trunk and then use a Bevel and Emboss FX to give it the slight roundness/highlight to give it some depth. Your tree is looking nice though. Much better than my first tree was.…