Normally I am against line-swapping too but really Babs hands are tied here. He has tried almost everything this season and nothing seems to be working.
Playing Datsyuk and Zetterberg on one line= opponents are going to focus on that line because they know, other lines will be just that normal lines.
Seperate both = they have to carry each line by themselves so in the end less firepower but a more balanced lineup.
Looking at the state of this roster, there aren't many other options for Babs right now. Other players have to step it up and provide some help to Z and D otherwhise the line-swapping will continue, because like I said Babs doesn't have a lot to work with.