Most executed pirates ended up buried in unmarked graves. If the place of hanging was near the shore, probably ended up being somewhere near the shallows. If multiple people are hanged at the same time, there's a good chance of them being burried all together in the same hole. If the government wished to make an example of the pirates to public, they took the bodies and gibbeted them with chains and/or iron hoops. Dipping in tar also is possible in this operation. The gibbited body is placed in a very visible public place, often in sight of maritime commerce areas. Once the body has been there for a while and rotted away significantly, then it was probably buried in an unmarked grave like previously mentioned. William Kidd and John Rackham (and two of his crew) encountered gibbeting off the top of my head.