The Groundskeeper reads in part:
While this is in play, when you gain a Victory card, +1VP.
Due to the shapeshifter errata in September/Oktober 2019, Overlord (and similar cards) no longer "become" another card, they just play the other card, but leave it in the Supply:
Play a non-Command Action card from the Supply costing up to $5, leaving it there.
Taking this together, this means that no Groundskeeper is in play in the scenario you described. That also means no Groundskeeper "gain VP" ability will trigger when a Vicory card is gained.
The shapeshifter errat made them worse with cards that have in-play effects, like Highway or Groundskeeper.