If you are keeping the starting battery topped up, you should never need to break out the generator but yes it will work. Note: the typical generator 12v system is only 8-10amp and it's unregulated. OK in a pinch but it will be slow.
It's not so much 6v vs 12v for CCA...it's deep cycle vs starting battery. CCA correlates closely to the surface area of the plates in the battery.
- The 6v golf cart batteries are designed for deep cycle use in golf carts. They have a smaller number of lead plates but the plates are thicker. There is no harm in using them for starting but they won't generate as many CCA.
- The 12v starting batteries are designed to put out a huge boost of power to start an engine and then the engines alternator is providing the ongoing power. They have more but thinner plates. The extra plates provide ore CCA.
