Under the ordering rules, contributions are first, and conversions and rollovers are second, and earnings are last. As far as I can tell, the entire amount rolled over is considered to be the rollover, and you don't separate the rollover into a rollover of contribution and a rollover of earnings. It's all "rollover" for the ordering rules.
@dmertz anything further?
However, I am puzzled by the idea of a Roth 401(k) match. Your employer can't match funds in an after-tax plan unless they include the money in your W-2 taxable wages, subject to federal, state, social security and medicare withholding. Normally, the employee match is pre-tax and goes into a pre-tax account even if you choose to make your own contributions to an after-tax account. Can you clarify this?
