Only if you don't want each zone represented. On most head units, you get sound in 4 channels (LF, LR, RF, RR). If you only run to 2 channels, you can do that, but only if you ignore either Left/Right, or ignore Front/Rear and only if your amp can handle the lower resist and bridge. In general, it's not a good idea.
You need a 4-channel amps or 2 2-channel amps if you want/need to amp all 4 speakers. I think the Rockford Fosgate line is pretty good performance vs. cost, but there are tons of low-power brands out there too, all depends on what the RMS need of your speakers are.