Depends on what you mean by 'harmful', I suppose
If/when you switch away from an Ergo, that will be one of the many things to re-adjust to, but if it's more comfortable for you why not give it a try?
I'm no ergonomics expert, but I've been using a Kinesis Freestyle split for the last few years with pointing device in the center to help with wrist/shoulder discomfort. I'm switching to an ErgoDox as soon as I can get my kit together and am also looking at colemak layout.
What do you think of Colemak so far?