There is probably a thread on this over at the SEAWORLD board but , yes we did this last year. There were actually several coaches all leaving SeaWorld around 9.00am. You need a Busch gardens entrance ticket to get on and I think the cost was about $10 per person return.
PS You may need to book a seat as it was VERY popular when we went in June.
Again you'll probably get more info on the SeaWorld board itself.