I have to say I have never tried to make an image of a software raid. It would make sence to presume, however, that you only need to make an image of one of your drives. And if you need to boot from it, it should behave as if the second drive has failed.
Ghost-11 should be OK, if you can load the correct driver for USB support. I have personaly imaged drives to external USB harddrives. I used Hiren's BootCD, which (the version I used at the time) had Ghost-11 on it with "USB support" option. When used, this option offered several different drivers to load and the main trick was to guess which one. On some systems I actually used the old USB-1.1 choice it has and it still worked.
It goes without saying that your system must have USB-2 to be able to complete that image within acceptable timeframe.
Hopefully it does, as I have a couple of HP DL580 servers, and, while they are quite decent systems, they only come with USB-1.1.
Good luck.