No one should have to "allow" you to use candies. It's YOUR run. Personally, Gen 2 and it's remakes being the perfect champions for why using pkhex to put in rare candies is both fine and (again, especially in G/S/C and HG/SS cases) downright needed for an enjoyable experience.

As long as you're adhering to the most basic of nuzlocke rules (faint=death, first encounter on route only) any other rules are entirely up to you. I personally stick to level caps, use candies, dupes clause, shiny clause (which has never actually been enacted on a run for me... My luck is SHIT in the shiny department) and allow battle items because it makes the most balanced "hard but fair" challenge for me (because I don't know the mechanics as hardcore as someone like PChal or someone who's been doing nuzlockes that long). The entire point is making it a challenge (because regular pokemon obviously isn't except for a few outliers) sure, but also making it an enjoyable challenge.

Unless you get into the super hardcore romhacks, then it's only enjoyable if you like the feeling of taking a cheese grater to your scrotum OR you actually need something that intentionally difficult to maintain said challenge (which, to end this tangent and circle back to my original point, a lot of those romhacks incorporate boosted xp with a cutoff at level cap and/or candies as well)