It would be cheap insurance for slightly longer longevity to put a coat of sealant or a couple coats of polyurethane on the floor. OTOH particularly if the floor is 2" planking I kind of doubt you will see a big difference unless you are around a looong time. (Assuming you keep your litter dry and clean).
However, I want to point out that putting vinyl down DOES NOT substitute for sealing the floor -- in fact, putting vinyl flooring down makes it *more* worthwhile to seal or paint the floor first. Reason being, realisticially the chances of your being able to prevent some moisture from gettting under the vinyl are very, very slim. Waterers DO spill, rain DOES come in the windows, walls or roofs DO sometimes leak, etc. The water can creep in around the edge of the vinyl or track under from below, really it can, and then the water is mostly STUCK there rather than getting dried out somewhat by the litter if you didn't have the vinyl. I would really really suggest a coat of deck sealant or polyurethane or paint under any vinyl flooring. (ESPECIALLY for those brave souls who think stick-on 1' squares are a good idea).
Just make sure the fumes have aired out real well before you put the chickens in. Like, aired out to the point where if you close the coop overnight, you don't smell sealer in the morning when you go back in.
Good luck, have fun,
Pat