Controlled group situation. Employer A and Employer B 100% owned by the same person. Employer B adopts a plan yet employer A does not. Lets assume 410(B) is not an issue. When an employee transfers from Employer A to Employer B who has a plan, does the employee receive credit for the service with Employer A and therefore would not need to satisfy the eligibility rules and would already have years of service for vesting requirements? Would you consider prior year compensation when determining Highly compensated employees?

Yes to HCE - check 1.414(q)-1T, Q&A 6.
Yes to service check 1.411(a)-5(B)(3)(iv)(B) and Labor Reg. 2530.210(d).