Does triac used for on/off purposes need RFI suppression?
Umm..how can I make this simple....

If you have a regular light switch and turn the light on and off, how much RFI does it make.... a bit, but not enough to worry about.

Now toggle the switch 100 to 120 times a second, depending on which part of the planet you live.... get the picture?

Dimmers work by doing exactly that at different points of cycle of the AC mains.



Each of those points in the waveform above where it switches off generate an RFI burst. This probably wont hurt the dimmer, but good luck listening to your AM radio.

As mentioned in the comments. Even using a triac as a switch, you are still better turning it on at the zero crossing point. It will create extremely little RFI, and also improve the TRIACs Life.

There is a suitable circuit here

Hot Line Switching Circuit