Is this a thing where once we put guys on LTIR to not break the cap ceiling, we have the overage all season regardless of whether or not it's needed?
Yes. And if I'm reading CapFriendly correctly, the Red Wings will actually "accrue" actual cap space most of the season because they will likely operate under their new limit (or ACSL). This is why teams finagle with oddball recalls and demotions before putting guys on LTIR.
It looks like Yzerman got the perfect storm with injuries to get as close to the limit as possible. Franzen, Zetterberg, AA, Ericsson, Daley and Nielsen on regular IR, and then recalling Svechnikov, Biega, Kuffner and Kaski (at whatever their prorated hits were after spending a few days of the NHL season demoted/with another team) got them to just $25.5k under the $81.5M limit. If needed, they can now go $10,037,878 over their ACSL of $81,474,570 for the rest of the year. If they get under the ACSL (which they did when Kaski and Kuffner went back down, and will further once a couple other players go down), they will gain cap space for the rest of the season.
I'm going to guess they took advantage to gain the most flexibility:
-They can add some big salary in a trade if they want
-With the opening roster salary and no one on LTIR, they had some cap space, but if enough guys ended up on IR (like 4 or more), they'd start to get limited in terms of being able to recall some of their higher dollar ELC's and would have to rely on the emergency exemption (which only allows you to recall guys with a cap hit of equal to or less than $100k over league minimum)
-The accrued cap from not going over the ACSL could absorb all or most of any performance bonuses for this season that might have otherwise spilled into next season