I have a VRS15 light switch (Leviton) showing up as an appliance module when I try to include it. Is there any problem with this, and is there a reason it’s doing so?
If by “appliance module” you mean the switch is showing only ON/OFF capabilities, that should be correct. VRS15, as far as I remember, does not have dimming capabilities, so ON/OFF is what you will see in Vera.
Yes, it’s only showing up as an on-off, which is correct. My question really was- why does it show up as an appliance module and not a light switch?
That sounds like just the generic name that was assigned by Vera. You can change it to anything you like by clicking the wrench icon and then click the name at the top that says “_appliance module”, when the box goes yellow just edit it with what you want to call it and then save.
A Z-Wave “light switch” usually involves some dimming capability. If your device can’t dim the lights, it’ll show up as an appliance module even if it’s an in-wall device used to turn on or off your lights. You’re free to rename it, as strangely said. 
Will a VP00R 1x work as a normal dimmer on a non-zwave circuit?
Any Z-Wave device with dimming capabilities can be used without being tied to a Z-Wave network. You obviously won’t get any of the networking benefits, so it handles just like any random dimmer.