Is the Jon Stewart show on Comedy Central on an extended hiatus?

The Daily Show and The Colbert Report are both in the second week of a two-week vacation. New episodes should start next Monday.

Yes. I think they do this every year, take vacations. No one else can be Jon Stewart or Stephen Colbert. I suppose they could find someone to sit in for Jon Stewart, though it certainly wouldn’t be the same, but Stephen Colbert is The Colbert Report; so if they want vacations, like everyone else, they need to stop production of the shows for a couple of weeks.

Almost every show takes a hiatus prior to May sweeps.

It is normal for both the Daily Show and The Colbert Report to take 2 weeks off prior to a holiday, giving them a little longer vacation.
I believe shows resume Tuesday.

Yeah, @filmfann might be right. Sometimes they don’t start on the first Monday back. Probably has something to do with giving the staff time to prepare.

Just a note: the official website now confirms that new episodes will begin Tuesday rather than Monday.