Sorry, just did a bit of research, seems it should be fine! I'm an Nvidia man so I'm not terribly up to date on Radeon GPU specs.
Give it a go and see how it does. There's a lot of fancy visual effects in ArmA if I remember correctly (it's been a while since I played it) that can be turned off to help out the GPU (things like motion blur and bloom which don't actually look very realistic anyway).