I've never heard of being asked by an employer to make an account associated to a non-work account (like a personal email). They should provision SSO, or at least use a company domain like apple.com or internal.apple.com for test accounts.

Day 1 at FooCorp: "Your email address is you@foocorp.com. Conducting business activities with personal accounts is against policy and may result in disciplinary action including termination. It may also be a regulatory violation depending on industry."