As long as it falls under historical reference in the game world then yes, with DoDS being a WW2 game its absolutely acceptable to have a spray with a swastika in it. Just use some common sense, is it offensive? is it historically accurate or relevant?
Also heres a tip that works for 80% of people out there (according to the 20% moron scale), if you want to use a particular phrase or image in your spray and you second guess yourself then more than likely you shouldnt use it.