Your client has a requirement that only employees whose user person type is "Regular Employee"...

Create a Participant eligibility profile and select User person type from Person Type under Employment.

Create a Participant eligibility profile and select User person type from Person Type under Personal.

Write a fast formula of type Participant and Rate Eligibility, get user person type from this

Write a fast formula of type Participant and Rate Eligibility, get user person type from this formula, and attach this formula to an eligibility profile.