Hi Diveron
No, there is no diving to speak of close in to Placencia...it is really necessary to get out to the reef for the best action, the boat ride can be an hour + each way.
Being diehard divers we elected to stay at a location as close to the reef as possible to be able to get in lots of dive time without all the boat ride BS. Thats when we came up with serende island resort.....www.belizecayes.com.
The have a small well equipped dive shop right on top of the reef...really nice (not the Ritz) but warm, friendly, comfortable private island.
Hope you have a good trip. They are in the low season right now, best times are Dec-April.