I believe once the party has requested a reexamination on the ex parte basis (hands off, literal translation) it is then up to the PTO to determine if a reexamination is warranted based on the requestors citing of prior art, obviousness etc etc.

Once those wheels start turning and the PTO sends a letter of decision, that a reexamination is warranted, then the party requesting the re-exam is basically out of the loop (except for a reply to the patent owner's statement) and the re-exam is under complete control of the USPTO. They take it to it's conclusion of voiding the patent, adding and/or deleting claims and terms and finally an issuance of the re-exam certificate.

From the USPTO..

If the request for ex parte reexamination is filed by a third party and not the patent owner, the third party may not participate in the ex parte proceedings beyond the filing of a reply to the patent owner's statement under 37 CFR § 1.530, if the patent owner files a statement. No other reply or submission by a third party will be considered in ex parte reexamination.

and...

The third party requester is not permitted to file any further papers after his or her reply to the patent owner's statement. Any further papers will not be considered and will be returned to the requester. The patent owner cannot file papers on behalf of the third party requester and thereby circumvent the rules.