The 'removeFromCRL' reason code indicates that the certificate is, in fact, not revoked. The idea behind 'certificateHold' is to make a suspension, not a revocation: the PKI declares that the certificate should not be used until more information is made available (in a subsequent delta or full CRL), while not fully revoking the certificate, because revocation is a one-way trip. In that sense, the certificate was never revoked, and thus was not "unrevoked" either.
This implies that the "revocation date" for a 'removeFromCRL' code is completely ignored. That date qualifies the instant from which the certificate should be considered as revoked, until the end of times; the 'removeFromCRL' code cancels that.
If you look at RFC 5280, you will see that the revocation date is not used at all in the validation algorithm. Its main purpose is to support past validation, when you want to know whether a given certificate was valid at some past date (this is used in some signature formats, in conjunction with time stamps). When a CRL lists that a certificate has been revoked at date T, this means that after date T the certificate must not be considered as valid, but also that before date T is was fine. For instance, if the certificate was on a smart card that has been lost, then the "revocation date" should be the last time at which the smart card was last seen by its owner, since at any ulterior date the card might be in the wrong hands. For the certificateHold/removeFromCRL pair, the point is that the private key was never compromised and the certificate never revoked, so there is no "revocation date".
(Arguably, the 'certificateHold' and 'removeFromCRL' reason codes are a hack which encourages PKI owners to use revocation as an emergency suspension mechanism, i.e. a substitute for authorization, and that is a bad idea. Revocation is, by nature, an asynchronous mechanism, and does not work well for that. When a situation arises where you would want to put a certificate "on hold", the sane thing to do is to revoke the certificate and issue a new one.)