As has been pointed out already, AMU is accredited, both regionally and nationally, so the accreditation is up to snuff. I have heard nothing but good things about AMU from the students I have chatted with. The course work is rigorous, and you will definitely get an education. I know that many military personnel have attended AMU, particularly for graduate degrees. As you can probably tell from the school's name, they are geared toward service members, and they go out of their way to cater to them.
In regard to Rip Off Report and similar web sites, keep in mind that these are what I call "b*tch and complain" sites. Your not going to read anything but complaints on those sites. What about the thousands of other students that don't have any problems at all? They aren't going to bother to post at Rip Off Report.com, so take what you read there with a grain of salt. No school is for everybody. You have to select the one that works best for your particular needs.