Mark,
ALL UV light is harmful, but the UV-A less so than the -B or -C. However, I would not work around an exposure unit that leaks light without proper eye protection. If you have a good sealed unit, they you probabla don't need to worry about it, but if you are going to be doing dodging and burning, you should be wearing eye protection and possibly skin protection, depending on the lamps you are using.
Eye damage is cumulative, so a lettle here and there is not going to be noticeable, but if you spend a lot of time around UV light, it will accumulate into potential problems later in life. That's not a tradeoff I'm willing to take, especially when good UV protection costs about $10 at the local home center.
---Michael