Does the patch or Dead Money fix the merchant glitch (where you sell them same item they already have, buy it back, and sell again for profit)?

Yes.

no, he just wants you to stop using it.

im not sure its exactly a glitch, they wouldve fixed it by now. same thing was in F3

Actually I misunderstood how he worded the question, I thought he was asking if the glitch still existed.

Most definitely not fixed.