Re:
If you get the GripShift branded grips then you'll find they will be a bit shorter than normal grips, they take into account the GripShift unit itself has a portion of grip on it.
You can however use normal grips if you want, this is what I prefer to do, it means you can give yourself a bit more room on the bars. Or you can cut the normal grip down to a length to suit you, whilst still having a normal length grip for the other side of the bars.
From experience, don't go for thick chunky normal grips, it might interfere with you operating the GripShift.
I've not tried GripShift with lock-on grips yet, but I don't see why that couldn't work with just the locking collar on the outside of the handlebars.