Nope. I've been using up to three monitors for years (RTG & Flickerfixer, standard RGB, A2024), there's no problem. As long as you're using different output ports, there's not even a remote possibility of damaging anything.
You can also connect more than one monitor to a single output - if you do that with a simple split cable, the picture grows a bit darker (due to several termination resistors in parallel), but there are amplifiers to get around that.
Actually, it's quite impossible to damage the 'video chip' Denise since the analogue RGB outputs are driven by the 'vidiot' hybrid (pre-AGA at least).
