It won't hurt anything, but it is dirty, it will leave "tracer goop" in the barrel, and over time can effect accuracy, and it's a pain to clean, but you can do it. If you do use them do the same thing the millitary does load 1 tracer every fifth round so you have 4 regular rounds, a tracer, 4 more regular rounds, them another tracer, and so on, this does 2 things:
1: It conserves tracers (and reduces the "line" back to you.).
2: It reduces the amount of "tracer goop", and the 4 regular rounds between them should get rid of most if not all the goop there is.