I guess it depends on what you are using the carbine for...
Our "tactical" weapons have flip-up BUIS, but also mostly run PACs or PEQs. We aren't blessed with PVS-14s as of yet, and are running PVS-7Bs and PVS-7As. It is tough to line up the single tube on those with the EOTech or Aimpoint, I have found at least.
The Patrol Carbines have fixed BUIS, on the theory that they are coming straight out of the rack and into action, and the user may not have time to turn the EOTech on, adjust the settings, or may suddenly discover that the batteries are dead (I know that the operator should be more "squared-away" and should check that at the start of every shift, but you really have to "grunt proof" these things). Those still have NV-compatible EOTechs, but that is only a function of logistics simplicity, namely, buying one kind of sight, and these are never intended to be used with NVGs.