will it interfer with my treatment?
That is an old wives tale, my Grandma tried that......it makes you drunk, not better.
Not necessarily. Although there doesn't appear to have been any scientific study of this, there could be something to it - read Christine Miller's post on this remedy. Another folk remedy that has been studied and found to have some effect is tart cherries and you can read more about that here.
That said, when taking methotrexate, it's important to avoid alcohol. I don't know whether the small amount of gin in the raisins would be a concern, but you can ask your doctor. However, given that there's some evidence that tart cherries work for inflammation, but no scientific study of gin-soaked raisins, maybe you'd be better off sticking to the cherries.