Certainly no issue with only having one pannier. In fact for commuting it makes much more sense to only have one bag to worry about than two if you can get everything in.
I've commuted for a good couple of years now with one Ortlieb that contains my full suit, shirt underwear and shoes, toiletries, and a towel. If I need to take anything additional - i.e a
Wiggle return for lunchtime posting, or my laptop, then that goes in the other side, but for general everyday commuting just one is perfect. You get over the weight imbalance in the first half mile of riding, and then won't notice it again.
Ortliebs back rollers are great by the way. Totally waterproof, hard-wearing, and very spacious.
I use a Tubus rack. Also very good quality and lightweight.