Unrelated employers with separate 401(k) plans in pooled account

[Guest TaxedToDeath]

First question: If more than one unrelated employer, each with its own 401(k) plan and trust, pool their trust assets for investment purposes in a single account at a financial institution, is this okay? This doesn't appear to fall under the requirements for MTIAs because the plans are not maintained by related employers.

Second question: If one employer with more than one 401(k) plan and trust pools the assets of all of its trusts for investment purposes in a single account at a financial institution, MUST this be treated as an MTIA (assuming all other MTIA requirements are met)? Or are trusts sponsored by a single employer that are pooled in for investment purposes in an account that is not an MTIA permissible?