(unfortunately) No. Or at least not in most of those clips.
I'm going to steal from smashboards and define a "true combo" as:
an "inescapable combo." So in other words, once you get hit by the first hit of a combo, you are stuck in it unless the attacker messes up.
In this case, that'd mean that once you've been grabbed, there is absolutely nothing you can do to escape being hit by an up-special from K. Rool.
In the clip you've posted, it's clear that the grabbed player was able to get out an almost full back-air (17+ frames), which would've been more than enough time to air dodge or jump out.
However, things look a little closer at this timestamp.
When you pop out of a bury, there's absolutely nothing you can do for the first 12 frames (I've just tested this). This means there's a small (1/5 second) window immediately after the grabbed player pops out of the bury where getting the up-special would be completely true.
Of course when they'll actually pop out is dependent on the grabbed player's mashing and their percent when buried. So I'd say it's "true" if you can somehow manage to perfectly predict when they'll pop out. But of course with how small the hitbox is on the up-special (as MBorg notes), the odds of this working perfectly and being inescapable are slim.
That being said, it still looks like a fun/stylish mixup option. If you've been consistently up-tilting out of down-throw, you'll have conditioned them to mash and jump out of the bury. Then you can catch that jump (or maybe a move they've thrown out that was buffered from the mashing--like that timestamp you posted) with an up-special.