I think you are missing the point. These are Homeland security people from outside FEMA. This doesn't mean that there were not also FEMA people being sent on a different schedule.
BTW, the reason I'm confident these are not FEMA people being requested is because they are told to check in with FEMA Human resources.
http://wid.ap.org/documents/dhskatrina.pdf
You are correct, as are all the people noting that FEMA is not supposed to be a first-responder -- they're not even supposed to be in-field until about 96 hours after the disaster occurred.
FoxNews had to issue a sort of correction a little while ago. Fox to its shame (with Catherine Herridge) had jumped on this FEMA "memo" report as some sort of smoking gun, too.
Fox's clarification was that the FEMA memo wasn't nearly as significant as the media were making it out to be because the persons Brown was addressing in it were only VOLUNTEERS -- not paid, trained rescue personnel.