With current Intel chipsets that have included RAID, I normally expect drives to be in AHCI mode even with RAID enabled until the drive is manually added to a RAID volume. I'm not certain how your motherboard/controller manages it.
In the event that it actually won't let you use a drive on a 'RAID' port as a normal AHCI drive, you should try installing the SATA drivers provided by ASUS here. It could be a 'FakeRaid' port, which would require the OS to have the appropriate drivers before RAID works.
And yes, single drive RAID is possible. Not normally done, since it provides absolutely no advantages over AHCI, but if your motherboard demands drives on that port to be in a RAID array, it is possible.
Possibly relevant is this:
He wanted to install an OS on the RAID drive.
So I do see a Marvell module. It is possible you would need to
configure a single disk as a "stripe of one disk" or something
similar, then do an F6 install of a RAID driver, to get it to work.
Now, when I look in the e2736 M2V user manual, it says:
"Do not install the operating system with the device connected to the
Marvell® 88SE6121 Serial ATA connector."
So that is not an encouraging sign. It implies Asus doesn't think it
As Bill said, give it a try, but there are no guarantees it will work.
It all depends on things like the RAID setup in the BIOS, the Marvell
driver and what it is capable of, and so on.
I have installed Windows via the SATA ports connected to the VIA southbridge, with no problems. (also had to swap the HD, the 160 Gbyte had some problems, now have an 250gbyte SATA)
After that I installed the marvell drivers (drive still connected to the southbridge SATA).
After all this I connected the SATA driver to the Marvell connector (the internal one) and it tried to reboot: Windows logo showed up but somehow the SBOD (the well known bleu screen) showed up.
My conclusion is: Booting from the Marvell connected harddrive is possible, as long you have the proper SATA drivers for it.