The Assad regime isn’t Islamist, indeed they are not even Muslim, but as Michael said, they are allied with Islamist Iran and promote Iranian interests, and they also support Islamist Hamas and Hizballah, including Hizballah’s takeover of Lebanon. So when discussing internal Syrian affairs it’s indeed wrong to call them Islamists, but when discussion matters from a regional viewpoint they are counted in the Islamist camp because they work very closely with the Iranian Islamists. That’s what people mean when they call them Islamists – it’s a shorthand for being in the Islamist camp. An Iranian cleric has recognized them as Muslims, which is very important to them since it supposedly gives legitimacy to their rule (according to Islam non-Muslims are not supposed to rule Muslims).

As for the rebels, I think only about 60% of the Syrian population is Sunni Muslim. The rest are Christians, Shiite Muslims, Alawites and Druze. So assuming the 40% who aren’t Sunni Muslims won’t support the Muslim Brotherhood (which is Sunni), and also not all Sunni Muslims will support them (the [Sunni] Kurds on average are less extreme than Sunni Arabs, and of course not all Sunni Arabs support the Brotherhood), some people believe the consequences of a revolution in Syria can be different and that there’s an actual chance for something more resembling a democracy. Personally I don’t believe a revolution in Syria will end well. Which doesn’t mean I hope for Assad to survive since this regime is terrible. It only means I’m not optimistic either way. But I hope I’m wrong.