Alright, so let's say I'm using a bisharp as my physical sweeper and mismagius as my special sweeper. Using the popular sets on smogon, none of them suggest using a band or scarf. Would that be acceptable for my team? Or should I have another pokemon with a scarf or band? Thanks.
your mindset is too formulaic. teambuilding is not as simple as "this is my physical sweeper, this is my special sweeper, this is my scarfer, this is my bander, i got two filler, boom does this team work?" the use of scarves/bands/specs/etc is broad and it's really not reasonable to assume that they are or are not necessary on a team. not all scarfers/etc are directly comparable and neither are the teams that use them. moreover, to say that they are would be rather misleading.
you should also consider why exactly the pokemon "don't have choice sets listed on smogon". bisharp and mismagius are both, not mincing any words, TERRIBLE in ou. moreover their choiced sets might be unlisted because they face competition from a pokemon that fills similar roles better. i'm not a UU expert, but just at first glance i do not see many UU speedymons that would make scarf mismag useful, where as say scarf chandelure is definitely a thing and packs more punch.
overall, your questions are good but misguided. there is no answer to the question "should my team have a choiced mon on it?" that's far too dependent on how you play and what your team is. however, the question "should every team have a choiced mon on it?" has a very easy answer - no. teambuilding is simply too open ended of a process to make such a generalized statement. the only proven method is to experiment and find out what works the hard way, although more specific advice is possible if your situation is more specific as well (ie list more mons, be more specific about how you want to play the team, etc).
EDIT @ BELOW: this is the OU sqsa thread, i assume every question is about OU. UU has its own thread if that's what he's asking about, but it's here, so that's what i'm going to work with