As Pes pointed out canines can have many of the same allergies we can, so would never hurt to try some latex contact first somewhere a little less Sensitive than the boy's red rocket, or go latex free.
Depending on what you're actually offering him to do with you, a condom might not be practical to that end. Condoms can be a nice comfy well lubricated way for him to hump into your hand, that also has the added benefit of all his doggy juices are kept away from the carpet. Condoms aren't going to work out well though if you're wishing for him to penetrate you, like say in the ass or vagina. If you were to slide his sheets back and slip the condom over his unerect penis, as soon as you let go, the sheath is going to slide the condom right off, and Its not safe to try and somehow wedge the condom inside his sheath. If he's been stimulated to the point, that the knot is keeping his doggy member out of the sheath he's probably already orgasm'd at that point.
But most importantly, if you know this dog so little that you don't even know if he's healthy. Sex with him, protected or not, is just a bad choice tbh.