You can still use the burn options of cards with a requirement he could meet when you play them, but does not meet while in play.

Cannot be treated as a Ventrue antitribu nor a Samedi while uncontrolled or in the crypt (eg. Coroner's Contact cannot fetch him).

The ability ability cannot be used to fulfill card requirements if they are not played normally, like when using Concealed Weapon for an equipment or Piper or The Summoning for an ally.

When meeting a requirement to play a card, the vampire is treated as such for all the effects of the card, and only them, including duration effects. The vampire is not treated as meeting the requirements for effects the card has from being in play.