Does playing a unit from the champion zone count for Red RekSai accelerate?

Yes, playing a unit from your Champion Zone counts for Rek'Sai, Breacher's ability, and you must pay the [Accelerate] cost if you want that unit to enter the battlefield ready.

According to RiftJudge FAQ #10570:

1. Granting the Keyword: Rek'Sai, Breacher grants the [Accelerate] keyword to friendly units played from anywhere other than your hand. Since your Champion Zone is not your hand, units played from it gain the keyword.
2. Optional Cost: As established by Rule 805.1.a, [Accelerate] is an optional additional cost of [1] Energy and 1 Power.
3. Payment: If you choose to have your unit enter the battlefield ready, you must pay the [1] Energy and 1 Power cost during the "Pay Costs" step of playing the card. If you do not pay this cost, the unit enters the battlefield exhausted by default.