1) Some might have been/are in Yemen, but maybe some were killed alongside Houthi allies during airstrikes?
2) IRGC sent Hezbollah advisers(just like iRGC sent Hezbollah advisers to Iraq and they helped make Iraqi Hezbollah) to Yemen, so in ME, Hezbollah advisers = IRGC advisers. Some IRGC solders/advisers were also caught in the PG in boats smuggling weapons to the Arabian peninsula. SO who says those iRGC "boatmen" weren't advisers who planned to deploy into Yemen?
3) Dont bet money there are NO IRGC boots on the ground in Yemen. Iranian IRGC are present in ALL countries Iranian proxies are present in- Iraq, Lebanon, Syria, so it makes sense they are in Yemen. Yemen is a large country and Houthis are fighting a big(relatively) regional coalition. IRGC are even more like to be present if Iran is dealing with a "new" resistance partner,because this partner is new and unpredictable, and untrustworthy(until proven otherwise).