I must say that i use Maya 2011 x64 and Octane and i have no issues with rendering RGB alphas, motion vectors, depth pass, normal pass, point position pass, they align almost perfectly. The only problem you can have is when you render in Octane with huge DoF or any DoF for that matter, this is almost impossible to match inside of Maya MR, but i have a good workaround for that also. You can render matte pass in Octane, it is tricky and tedious to setup but it's totally possible, maybe i'll share this later, make some tutorial, but for now it's a secret
All the best,
Voja