Is it an on-board RAID (motherboard provided feature) or PCI-E/PCI-X/PCI card? If it's MB, then no way it can be used by OS X/Chameleon as this type of RAID is not true RAID as such, it's more like software RAID.
Another question, albeit related to the first: if i clone the OSX installation from the external HDD to an internal one, will it be able to boot, despite SATA mode being set as RAID? Or OSX and Windows RAID arrays cannot share the same space?
If the external USB3 HDD can be disassembled (HDD removed) and the disk inside the box is a true SATA disk (with SATA interface, as there are 2.5" HDD used in USB external disks, that has a build-in USB interfaces and have no other interfaces except USB connector; Samsung, WD for instance), then you could simply install it to your PC and use it at once. I did this in the early days of may hackintoshing days
It was an IDE disk in fact, installed OS X to it via USB enclosure then put it back to PC, and booted. So no need for cloning...
...this computer have also Windows 7, installed on a RAID array using two SSD disks, and when i try to boot it from Chameleon, i get a "no bootmngr" message. I have to resort to hit F12 and change the boot order to access Windows. How do i solve this? RAID is not a realm where i really feel comfortable.
There is Chameleon version that can work off the Windows drive, but I'm not sure it will be able to function from within RAID volume. You can use a third boot loader such as GRUB to chainload both OSs (provided the RAID you're using is supported by GRUB).