It's a radio system use for missionary work in third world countries.
We are not too worried about breaking FCC rules since we will be using
them outside the US. My concern with the harmonic frequencies is mainly
protecting the transmission system and also not interfere with other
sister stations. From what I've read so far, some harmonic frequencies
might couple to the transmitter input and that can affect the output.

I guess what I really don't know about is how exactly harmonics affect
the system... and if a DSP based transmitter would also need these
bulky harmonics filter.

Hmm..also, wouldn't the harmonic filters normally be part of an antenna
tuning unit?