It is if you coat it with a two-part clear. I've used spraymax two-part clear with very good results. You MUST leave the filler neck free of paint where the fuel cap comes down though. Otherwise fuel gets under the edge of the paint and lifts it. The same goes for the fuel valve.
The spraymax goes on VERY evenly, looks nice and wet afterwards, and doesn't run/drip. I've been really impressed. I had some extra left over and cleared a friend's car roof since the clear was peeling off. It brought back a nice, clean luster to the paint.
By the way, the original stickers can be pricey to replace. You can tape over them before painting, and they will look good afterwards. I didn't bother taping, and just sanded the paint off after I painted my tank (I found some metal fleck rustoleum that matched the factory red perfectly, so I just buffed the original paint and painted it) with wet 400 grit paper. It looks fantastic, and has the original, worn pin striping for that vintage look. I cleared it with spraymax afterwards, and it holds up to gasoline just fine. The spraymax offers UV protection too, which will be an issue for any rustoleum paint you use.
Here's a short list of paint capabilities that I've found:
1) any single-part paint sold in stores will NOT resist gasoline, but will likely resist UV.
2) any single-part clear coat sold in stores will NOT resist gasoline, but will likely resist UV.
3) rustoleum WILL resist gasoline, but will NOT resist UV.
4) any two-part clear SHOULD resist both gasoline and UV.
5) any two-part paint SHOULD resist both gasoline and UV, but really should be protected with a two-part clear.
So, in conclusion, you can use just about any paint you want with decent results as long as you cover it with a decent two-part clear. You can either mix the clear, or use a pre-mixed can, but it must be two-part.