Is it possible to run an exit relay through a VPN service? As long as the service provider has approved this, is it otherwise workable? Do any technical limitations or performance disadvantages make this unworkable? Assuming that there's adequate bandwidth, is the increased latency problematic?
I believe you can do this if your VPN provider allows it, however it seems like would de-anonymize your traffic as all exit traffic would be linked to you (if it's your VPN.) You of course could argue that you were running a relay so the traffic isn't yours, etc.
Now if you're asking if you can connect to your VPN via tor, then this is very bad unless the VPN has nothing to link you to it, like a credit card, etc.