Does the US Army use Paintball to train?

Answer 1

Not with paintball guns, no. There is some use of Simunitions for urban warfare, but those are modified upper receivers on standard lower receivers. Paintball guns would be useless - hopper capacities don't reflect magazine capacities, the ergonomics of a paintball gun don't match the ergonomics of a service rifle - they'd have little training value, especially when an important part of the training is to familiarise yourself with the weapon you'd be using in combat.