Why? He hasn't played like one since he left Montreal 3 years ago.
We haven't learned anything if this guy is anything more than 8/9 on our depth chart, and even then, I expect him to be passed by guys like Kral fairly early in the season. Benn is this year's Biega, nothing more, and the only reason I can think of him getting a one-way deal (and same with Mete) is so we have zero risk of him getting claimed off of waivers.
If we are trading Holl, it is to get Sandin more ice time and we would sign a guy who can legitimately be a #7 defenseman (Hagg, de Haan, Subban, Stone, or Stralman).