Certainly, being good at pool already will quicken the learning curve for trick shots, but there is more to it than that. Most good pool players will have a decent stroke, good aiming, and can control the cue ball. To be a great trick shot artist, it takes a monster stroke, ability to make fine adjustments, and coordination (think speed shots or one-handed shots). One of the biggest weaknesses in my pool game is the ability to control the cue ball. I tend to overhit it because I'm used to juicing it up so much for trick shots.
So, next time you see a trick shot artist, don't be so quick to assume they're great at pool. There are a fair number that made the crossover from typical pool to trick shots, but there are plenty of others that became trick shot specialists without developing their general game.