I would say the only problem with that is the saturation level of salt into the water. If you are filling a 150 gallon tank then a 5 gallon bucket of water is not going to dissolve that much salt. If you are doing a 20 or 30 gallon tank then yeah, it would probably not be a problem.
I would also not shoot for 100% of the expected salt. I would go for 90 or 95% of the salt and then take a reading of the salt level in the tank once it's mixed up. Then add salt to bring it up to level. That way you are not having to pull out water and adding more water to bring it down to level if you got in too much. (no use in wasting it.)
Tim Sapp