Q: Is it possible to use a router table as a jointer?

John Brock: Yes, a very narrow jointer, good for edge joining but too narrow for face jointing. Make sure your infeed and outfeed guides are long enough and rigid enough, then you can set it up like a jointer laid on its side.
John Swanson: It is very easy to joint a board on a router table. It requires a straight bit and an offset fence. Make multiple passes, cutting on the left side of the bit until the edge is jointed.

Richard Jones: Yes. You can use an inverted table-mounted router to straighten narrow edges. Offset the outfeed table by the depth of cut set by the infeed table.

Carol Reed: Not only is it possible, I wrote an article showing a jig to do just that in the December 2004 router issue of the Woodworker's Journal print magazine. The jig is 60" long, allowing adequate support both on the infeed and the outfeed. This works well for edge jointing but not face jointing.