Now that I got some sleep, I woke up and realized that I said the wrong stuff to you, went back and corrected what I said.
On all disposals, the top connector is for dishwasher hookups, the second lower hole is for the drainpipe. If you remove the disposal, you can get a $4 'Y' pipe and put it in place of the disposal....I can take a pic of my setup if you want. You might have to do some cutting and/or replacing of the pipes.
As for that vent....I suspect that the building inspector might have ordered the plumber to put it in....possibly because the venting behind the wall was done incorrectly. A lot cheaper to put one of those vents in there than ripping walls apart. That vent has a check valve in it....only allows air to be sucked in, and not leak out.
Then again, I could be wrong....it might be a code in your area.
As for that outlet under the sink, if it was put in back in 2006, it is most likely connected to the GFCI receptacle you have above your sink, so it would already be safe. You can test it by pushing the test button on the GFCI and turn the disposal on, if it doesn't come on, great.
