dottybacks and grammas are conspecific, meaning they look a lot alike.
Dottybacks are extremely aggressive while Grammas really are not unless defending a nest.
In my Marine Fishes book by Scott w. Micheal, it specifically says do not put these two fish together because the dottyback is extremely aggressive...
Heres a link to someone who tried to do the same...
http://www.reefland.com/forum/marine...need-help.html
I wouldn't try it.