Is there any reason why that wouldn't fully protect them from legal risk if they wanted to visit the US personally?
(Though I would guess you probably can't do that retroactively.)
And US courts do "veil-pierce" through entities set up for the sole purposes of evading investor liability. (It's complicated to explain, but in a very simplified nutshell if an entity is set up for the sole purpose of evading liability for criminal acts, regulatory violations, civil torts, or responsibility for financial losses, then the courts will disregard the legal entity and just go straight to the owner(s).)
0: https://en.m.wikipedia.org/wiki/United_States_v._Elcom_Ltd.