Vow of Poverty, only clause I have is that we use my interpretation of the potion bit.
The Vow states you cannot ever use a magic item, own a magic item, or possess a magic item. The Vow states that another character can use a magic item (such as a wand or scroll) on a character. Included in the examples of items that another character can use on the Vow of Poverty character is a potion of cure light wounds. My interpretation is, the one I believe is correct, is that the only way a potion of cure light wounds can be used by another character on the Vow character is by applying the potion to a downed character as a full-round action.
If there are any questions on that, or if I didn't explain it very well, just ask.