Does hoodia interfere with coumadin/warfarin?

No. I can find no report of a drug interaction. You should be aware that many products marketed as hoodia actually have no hoodia in them.
Yes. Hoodia inhibits the cyp3a4 pathway, a common metabolic pathway for pharmaceuticals. In addition, there can be competition for protein binding which allows more of drug to be active. Recommend - use herbals cautiously or not at all with warfarin. May make control of anticoagulation even more difficult than it already is.