Vegas will need to be cap compliant on Day 1 of the season unless Tuch isn't expecting to play at all in the regular season. Kucherov is the best example.

is that the case, or do they just have to create cap room for Tuch right before he is ready to return?
in theory, they just need to trade Smith in parallel to Tuch's return, no?

So, the 1st link below is my source. It's the NHL CBA. The most recent update is really just an extension and some edits to the original one done back in 2013. You are allow 10% flexibility in the offseason, but the day the season starts...you need to be cap compliant. Kucherov was a loop hole because he never played in the regular season. Seabrook will be another loophole. He's not comin back either.
https://www.nhlpa.com/the-pa/cba

Page 261 discusses the upper limit of the cap.

(ii) Upper Limit.
(A) With the exception of the 2012-13 Upper Limit, as set forth in Section 50.5(b)(ii)(A) above, the Bona-Fide Long-Term Injury/Illness Exception set forth in Section 50.10(d) and the Performance Bonus Cushion set forth in Section 50.5(h) below for all League Years under this Agreement, no Club shall at any point during a League Year be permitted to have an Averaged Club Salary that exceeds the Upper Limit of the Payroll Range.
(B) Nevertheless, in order to ensure that Clubs may have sufficient time and flexibility to plan their rosters during the off-season, the Upper Limit shall be temporarily raised by ten (10) percent to permit Clubs additional flexibility with their Averaged Club Salaries during the period from July 1 until and including the last day of Training Camp. On the day following the last day of Training Camp, the Upper Limit shall again be lowered to the level as calculated in Section 50.5(b), and all Clubs must once again be in compliance with the Upper Limit from the day following the last day of Training Camp until and including June 30.

BUT, If Vegas truly wanted to lawyer up...MAYBE there is a way they can argue that the daily accruing of the $2M in cap space will eventually be sufficient to fit in Tuch's Cap hit. I don't see that as a winning argument, but that's what lawyers are for.

I wish the NHL and PA would just finally agree to pick a salary cap number that includes everyone....short term injuries, LTIR, EVERYONE! This daily accruing cap $$ is garbage. Trading for guys who will never play again is garbage. And the Kucherov "episode" wouldn't matter. You know it's a problem when teams have to hire a specific employee who is used for nothing more than the salary cap juggling act. And for us fans, it's a total headache.

One number. All in. Simple math. Do it NHL.

i don't think this is correct. with Tuch on LTIR, Vegas will be cap compliant.
in order for Tuch to come off LTIR they will have to move some money...

this is my interpretation, i could be wrong, but i don't think i am.

I'm actually having this exact conversation on another post too. So if grammatically something does read accurate...sorry about the grammer, but the CBA does go into illustrations. See below.

I'm going to quote the CBA and put in BOLD a few parts to keep in mind. Page 291 goes into examples of different kinds of LTIR situations. Obviously the cap amount adjusts based on the year.
https://www.nhlpa.com/the-pa/cba

Prior to Opening Day Illustrations:

Illustration #4: The Upper Limit in a League Year is $70.0 million. A Player who has an SPC with an Averaged Amount of $2.0 million becomes unfit to play on the last day of Training Camp, and on the same day, his Club exercises the Bona-Fide Long-Term Injury/Illness Exception on such Player. On Opening Day, the Club has an Averaged Club Salary of $71.5 million (excluding Earnable Performance Bonuses up to the full amount of the Performance Bonus Cushion). The Club is deemed to have already fully replaced the unfit-to-play Player with any Player or Players on the Opening Day Roster. If these replacements are maintained through the conclusion of the season, the Club's Averaged Club Salary is $71.5 million, as the Club is permitted to exceed the Upper Limit by $1.5 million because of the Bona-Fide Long-Term Injury/Illness Exception.

Illustration #4 is the "summer" LTIR method. If Tuch is sent to LTIR on the last day of Camp...summer...then Vegas has reached the cap ceiling. Where is the cap space to bring him back during the season? If we copy the illustration above, but put in exact values. $81.5M limit, but a current cap hit as of today is 82,737,439...THEN Tuch gets sent to LTIR on the last day of training cap with a cap hit of $4.75M...Vegas enters the season with a cap hit of $81.5M. They don't have any place for him to come back when he's healthy.


***EDIT*** The only way I see Vegas being able to keep Tuch on the Roster is actually a bit of a role reservsal. Max out the # of Slide eligible players on your roster while also keeping everyone you intend to keep. THEN send Tuch to LTIR in the summer...THEN slide down everyone you play on sending to the AHL. Maybe that's an option.