Agreed but it won't.
Leafs will go over the cap as much as Dubinskis cap hit. So as long as they meet the 81.5 cap for everything else, they should be fine.
It will hamstring them. They can't do what you are saying. Their effective cap limit would essentially be $75.65M (The maximum cap - Dubinsky's cap hit) as LTIR is not free space, and that's not how it works.
To be able to use all of Dubinsky's LTIR, the Leafs would have to get as close to the $81.5M cap as possible (setting the ACSL) on opening day
with Dubinsky and his cap hit on the active roster. So the Leafs would have to make cap clearing trades to fit Dubinsky's cap hit under the $81.5M limit, since
all NHL contracts above the buriable limit count towards the cap and must be counted.
So the Leafs would be required to trade away cap totaling at least $5.85M just to fit Dubinsky under the $81.5M cap on the opening day roster, and then he can be put on LTIR.
Now it should be obvious that the problem is the Leafs already traded away the very players they would have liked to add using the LTIR (in cap clearing moves) just to fit Dubinsky on the roster and be cap compliant, as teams can't just leave players (and their cap hits) off the roster and then add them in later. Every dollar over the buriable limit on every NHL contract counts towards the cap on opening day.
Hope that makes it clearer why this won't, nor should it be done. Plus they don't accrue cap space over the season either if they are into LTIR.