I wouldn't necessarily glue it - it may not have been designed to go up there (I haven't pulled a headliner yet,) and if it isn't, then pushing it out of alignment may not be doing you any favours.
If it's got a little flex to it, then it's probably in its "natural" position and should stay there. If it feels strained, it's a good idea to find out why.
If it's in its "natural" position, the most I'd do would be to put some Neoprene sheeting or some expanding foam in between the support and the roof (the roof is a "shear panel" in this application, and helps the roof halo hold its shape. The support is a crossbeam, and designed to make it a little more rigid) to make sure that the support stays put and that the two parts don't decide to start bumping together for some reason.
Of course (and I may be missing this in the pix - I prefer to take a more direct view whenever possible...) if there is any residue of adhesive or weld left from earlier, then it should be tacked back into place. I don't know if GG will do the job (has anyone tried?) but there are some "body shop" adhesives out there that can be used for non-structural repairs like this. I wouldn't use glue to stick a fender back on (although there was talk of using Velcro on Corvettes years ago...) but it will work for sticking one part to another. Why not GG? I don't know how flexible it is, and that application would certainly want to allow for some flexion...
5-90
