I think the risk of somebody hacking into your IM program is pretty minimal. It's not something I would allow to have any bearing on my decision to appear on cam or not.

Anyway, regarding the original question, I've come across several dommes over the years who were happy to work without webcam or pictures, without looking all that hard. And sure, there's a place for trust and imagination... on the other hand, if you really like to be forced and pushed and manipulated, then webcam is absolutely wonderful.