Colleges don’t care what you’ve skipped- they care about what you’ve done.
So if skipping means missing out on foundational courses that would allow a kid to advance in a traditional HS curriculum- then probably not an optimal idea. If skipping means less time to explore different EC’s, artistic accomplishments, athletic activities etc- then keep that in mind.
Will missing 9th grade impact the foreign language/math/lab science progression? I’d start there.