Since 1.5 and Horizons will release at same time will the beta's be together on the same server?
I don't know the answer to this for sure, but my guess would be that Horizons be released on a copy of the galaxy which will not be interactive with the non-Horizons galaxy.
I'd like to add a related question to this. If my assumption is correct and there are two separate galaxies, will players who own both games be able to play as their same commander on both games but have deverging player statistics at the point of the split?