Yes, Security Guard Knuckles is in here, but he is only summonable by the protagonist ~ Silent "Player-On!/Avatar-On!" as Comrade and for a limited time. (Doesn't mean you can do this in the game, this ability applies to the fancomic)

In this fangame, you play as the "lost wandering kid" moving around the pizzeria:
"The Player" herself.
(For the remind: Silent's "Player-On!/Avatar-On!" age is based on Gregory's age from Security Breach, i.e. 13-14. Because the protagonist from Fierce Forces is supposed to be based on the protagonist from Security Breach)

Overall: The plan from the beginning, for this unofficial FNaS series was to be the equivalent of FNaF Help Wanted 1 and 2 (dealing with the previous cast from all installments in one place) / FNaF Security Breach (the pizzaplex) mix.

Also the new name of the pizzeria in Fierce Forces "Imagine It!" (FanComic):
Sonic Heroes Tera Pizza Piazza
(in here: the word Piazza has the meaning of an arcaded and roofed gallery)

Because in the fangame something has happened and the protagonist is still in the big pizzeria, yet in a different spot and the new place's name.

The end of the partial spoiler.