Thanks Asper, you're right about the lose track thing for discards, I forgot about that. Man, that pesky lose track rule. I found a fix for trashing situations, but it breaks discards. That's too bad.
Well, let's see then, if my understanding of the lose track rule and the blue dog rule are correct, then Undertaker's current wording (with "reveal from hand" added) basically "breaks" any card that has a discard-for-benefit effect contingent on the discarded cards (Cellar, Storeroom, Vault, Mill, Artificer, Hamlet, Stables, etc.) or trash-for-benefit contingent on the trashed cards (Remodel, Replace, Trading Post, Upgrade, Salvager, Bishop, Expand, Apprentice, Forge, Remake, Develop, Farmland, Trader, Mercenary, Procession, Graverobber, Rebuild, Stonemason, Butcher, Raze, Catapult, Sacrifice, etc.).
It does still "work" with any card that discards or trashes without a contingent benefit as Fragasnap explains, but the above list is a hefty chunk of cards, including many interactions I had been excited about. I'll need to keep thinking about if there's any concise way the card can still somehow allow discard-for-benefit and trash-for-benefit cards to function normally while activating Undertaker's ability, without getting snagged on lose track and blue dog stuff.
Don't worry LibraryAdventurer, I won't ditch it just yet, but I would like Undertaker to function with more than it currently does, if possible. I feel like there's got to be a way to do it--it's a pretty simple effect to understand conceptually, it's just a matter of getting it to be worded such that it still abides by the rules of the Dominion universe. Anyway, thanks folks for the help on this one so far!