I have not done this with dotLRN, but I have had several ACS sites (ACS Classic, the old stuff) using the same data. It has worked just fine. So I would say that yes, you could do this, but my guess is that using subsites is a better way to achieve what you are after. I can think of a lot of unexpected user experiences you would get from running two dotLRN sites off of the same data, that are not a problem with our older sites.
