If they simply ask, "Are you a DVC member?" then answer Yes, because you are and answering No would actually be dishonest, you just aren't supposed to get the perks when you buy resale (which I think is silly anyway). If they ask a follow up, such as "Did you buy resale?" answer honestly. Same goes if they ask to see your member card, be honest about it.
Disclaimer: We did not buy resale, but I still feel this is accurate, as I said I think not giving the perks to the resale market is silly, but that's Disney's policy.