That's what I did...there is a concern with wireless odometers that they don't have sufficient range to receive a signal from the sensor if mounted on the back wheel, assuming you want to mount the display in the usual location on the handlebars, but it could work. That being said, I was lucky my cord just barely reached... It's such a tight fit it makes my bike difficult to steer on the road, although that's not an issue because its a dedicated trainer bike now.

As far as the need for an odometer, I don't think you can compare "miles" on a trainer directly to actual miles, but then again, its hard to compare actual miles to actual miles (when different routes and conditions are factored in). I find "miles" to be a useful metric to compare total exertion among different trainer sessions, as I keep tension and tire pressure relatively constant.