I would suggest contacting your 401k provider. They should be able to provide you with any regulations/rules in regards to employer matching.
We have a 90 day wait for participation in our 401k plan. We start the employer match at that time with the employee being 100% vested in their contributions and on a vesting schedule (100% after 6 years) for the employer matching. I do recall seeing language that if the waiting period for employee participation is 1 year, then the employee is 100% vested from that start date.