Keeper of Night, thing is, Weavile has 90 HP, and it effectively requires you to get all 4 Exeggcutes in your hand, and ultimately to the Graveyard. That does not work as well when some of them are prized.
And what of OHKOing EXs? You'll either need a Tool Scrapper handy or you'll need to discard up to 7 Pokemon - 6 without. That leaves the question of what the last 2 will be, and you can't always guarantee they'll be in your hand. Ho-Oh could work for that, but the problem is getting it into your hand.
It's fun on paper, but it'd require running a lot of other Pokemon to make it work. I suppose you COULD slip it into Ho-Oh, but it'd require a lot of work.