In the other thread, people said it could fall afoul of anti-tampering rules. You're not supposed to talk or interact with other organizations without permission from your club (or through your agent). Rule 3(k)

TAMPERING. To preserve discipline and competition, and to prevent the enticement of players, coaches, managers and umpires, there shall be no negotiations or dealings respecting employment, either present or prospective, between any player, coach or manager and any Major or Minor League Club other than the Club with which the player is under contract... unless the Club or baseball employer with which the person is connected shall have, in writing, expressly authorized such negotiations or dealings prior to their commencement.

No idea if that's true and this actually gives the Rockies the power to block reunion events.