So just got done with my AP with VGC/OV experiment. Did the whole put in a wrong expiration date for the OV when initially added to Amazon and then put in the correct expiration date for the OV. Went to onevanilla.com and verified that it didn't put a $1 hold. However I did see a preauthorization transaction from Amazon.com with $0 so that was good news. Just sent a $500 AP transaction and was completed successfully.

I don't know about the monthly limit being reduced but my guess is that since the transaction didn't officially complete on record, it shouldn't and your funds will be refunded back to your VGC.