Does Gitlab have a list of certified experts to oversee a project? My question may sound a bit strange, but I want to know if Gitlab takes responsibility for project confidentiality if one of these experts would be applied in my project.
Closest to that would be GitLab Professional Services.
Other than that, no, GitLab has no list of certified experts in that sense (probably something like that would be GitLab Team Page).
And definitely no, other than Professional Services mentioned above (and maybe some other official GitLab offerings), GitLab would never take responsibility for actions of people outside of GitLab.