^ Apparently so. Otherwise the "slowly digested over a thousand years" would be irrelevant to the victims. Given that Threepio uses this line to scare people about to be fed into the Sarlacc, then it must logically keep them alive that long, otherwise the threat would be meaningless.
The Star Wars wiki also says that the Sarlacc keeps victims alive all the time it digests them. Doesn't say why or how it does this, only that it does.