How necessary are Scruggs tuners when playing Scruggs-style banjo? They seem like something of a novelty to me, and I'd rather just not install them or learn how to do it, but don't want to leave it out if it's an integral part of a Scruggs-style banjo player's toolkit?
It depends on the song. Many out there can play Earl's Breakdown without them, even though it was originally recorded and played with Scrugg's tuners. The part that uses them is minimal (less than 2 measures long) and is easily yet accurately spoofed.
Now a song like Flint Hill Special, as mentioned above, has a much more demanding Scrugg's tuner dependency. They are used constantly for almost 8 measures straight, so faking that would require a bit more mustard and creativity.
If you want to specifically add those types of songs to your professional repertoire, I would suggest getting a set of the Scrugg's tuners. If you want to just 'get by' when those songs happen to arise, you can certainly find ways to do that without them.
You can't do Flint Hill Special without them, but you don't have to play Flint Hill Special. I don't think I've heard Bela Fleck use them.
Scruggs-style definitely does not require Scruggs tuners. Bill Keith also invented a similar device, but those are not required for "Keith style" (melodic) banjo playing. Even Scruggs rarely used them in his playing, and most listeners would not miss them except for on certain songs.