Other than Fowler and Dumoulin, Vaakanainen is the only veteran LD on the roster, and we knew he was behind those guys on the depth chart. LaCombe probably doesn't qualify.
Vaakanainen is in a battle for a 3rd pairing role or at least to be the 7th d-man. I don't think his presence on this roster is an indication that he's lower than that. The guys he's competing with for that spot (LaCombe, Zellweger) aren't veterans.
If we include Minty, although he's not ready for the start of the season, with Fowler and Dumo, then Vaak doesn't have a starting spot at LD.
Things get crowded very fast if we add Luneau into the NHL roster. Without Luneau on the NHL roster, then we have only Gudas at RD. Then there are starting spots available for Zell and LaCombe to play on the right side. With Luneau on the NHL roster, then one of Zell or LaCombe is off the starting roster or both will be in constant rotation. A rotational role for either Zell or LaCombe is not ideal.
Both Zell and LaCombe are waiver exempt. LaCombe has 73 NHL games under his belt. iirc, LaCombe loses that exemption after playing his 80th NHL game. For Zell, he's got until age 23 or played 160 NHL games to lose his exemption, whichever comes first. Should Luneau be in the NHL and one of Zell or LaCombe is sent down, then it helps Vaak secure a #7 spot on the NHL roster.