Yep, I'm pretty sure it would support SLI
And by the way, any graphics card thats PCI-E would work in those slots by any make, though not when running in SLI, as that is only Nvidia
There is CrossFire that is an ATI version, but I'm not sure how good that is in comparison, and this would also work in the slots you have.
SLI needs two of the same card though. As long as you know that, theres no problems.