I don't know anything about Yeo. I like the Zigomanis & Fraser re-signings - particularly Fraser because he provides some depth for the NHL team on D and he's the only really tough physical dman the Marlies had.
AHL Vet rule:
Of the 18 skaters (not counting two goaltenders) that teams may dress for a regular-season game, at least 13 must be qualified as "development players." Of those 13, 12 must have played in 260 or fewer professional games (including AHL, NHL, IHL and European elite leagues), and one must have played in 320 or fewer professional games. All calculations for development status are based on regular-season totals as of the start of the season.
Zigomanis, Hamilton, Orr & Aucoin have played more than 320 pro games in the regular season.
Fraser, Kostka & Yeo have played more than 260 reg season pro games but less than 320 so any of them can play as a 6th vet.
So if they're all healthy, one will have to sit out.
Assuming the Leafs add some sort of goalie, the Marlies seem as good or better defensively than last year when they were one of the top defensive clubs in the AHL. Adding Aucoin strengthens them down the middle and improves them offensively.
I would guess that they'll add Ross & McKegg from the CHL and maybe Carrick & Devane (if they're not ECHL bound). There's a decent chance this club could be better than last year as Mueller, Dupuis & Mikus are the only ones who played more than a 1/2 season that have departed with Kadri having a good shot to crack their NHL line up (or bust). I think the Leafs may add a 7th dman to try for depth so Holzer or that dman will play for the Marlies.
Of course, some of that could get shuffled with a trade and I also think that's very likely. Regardless, the Marlies should be a good team next season.