We've had interesting experiences with the Dell ESeries as well - ours, though, was related to forcing USB support through SafeBoot, which conflicted with the BIOS USB support feature in the ESeries. Anyway, be advised that you should leave the "Force USB Support (auto otherwise)" option disabled in SafeBoot on these devices on version 5.1.3, and on rev 5400 and 5420. Rev 5500 seems to fix it, although we are still investigating "why" since it was not listed in the changelog.
In related news, we are going ATA mode on those ESeries rather than higher emulation - and I think IRRT would be incompatible with Full Disk Encryption products anyway, wouldn't it? I haven't read up much on the technology but from what I've seen so far the two are incompatible?
IRRT mode may work as it is intended to see the drive in a docking station and mirror it, the drive in the docking station would be considered internal by safeboot and be encrypted as well, but raid and the recovery of data in raids is not supported by Mcafee Endpoint, but it may work. Have you tested an upgrade of 5.3 to 5.4 or higher and exprienced the same problem I listed?
I haven't yet - we were just trying to get the pre-boot environment working properly on the ESeries with 5400 / 5420 and I haven't had a chance to test the upgrade. Definitely something I need to try though. However, our corporate standard I believe is to go with ATA mode due to restrictions in our imaging software (that came straight from my local rumor mill, not something I have witnessed firsthand), so we may not run into the same issue you are seeing. If I'm able to test it out I will post back here with the results!