He needs a role while they wait out Josh. I think that BB asked Josh to forego a job last year because there was nobody ready to step in if he left. Daboll has been an OC in the league, is a very smart guy and in my mind was brought in as insurance should Josh get a job elsewhere next season.
BB's kid is already assisting McDaniel's with the QBs and Daboll probably didn't want the receivers again so the OL makes sense. He's going to learn a lot if he is in fact Dante's coaching assistant. he may be a roving assistant though, helping out all over the place as needed. It will be interesting to see what role he carries once training camp kicks off.
I'm hoping it isn't that he is taking over for Dante any time soon. I don;t want that guy going anywhere.
Daboll has coached QBs, RBs and WRs (presumably including receiving TEs), but I don't know that he's had direct, hands-on experience working with the OL except perhaps peripherally as an OC. So, working with Scar may represent the last stop on his "training tour" of all the offensive units.