First post here guys... anyways, have you guys been using anything from lower tiers in OU with success? I've been running a Scarf Darmanitan and Togekiss fairly well, as well as Nosepass as a lead.
OK, this is your first post so welcome to Smogon! Now, i will try to address what you said. First of all, there are many pokemon from lower tiers that are good in OU, all BL mons are viable (unless they decide to ban Salamence from UU), a good number of UU/BL2, RU, even NU and PU.
Nosepass is awful, any FEAR tactic will end up being a huge gimmick instead of having a real pokemon on your team, the strategy is obvious and is an old trick that noboy falls for, they will just bring status, multi hit moves and hazards destroy it, it is just a failed strategy that most of the time does nothing, don't even bother with it.
Darmanitan isn't terrible but isn't very good in OU, it is mostly outclassed by other fire types such as Entei and Victini but Scarf Entei is terrible and Scarf Victini isn't great in this meta so Darmanitan may be a better Choice Scarf user than Victini, it has no weakness to Pursuit and that's important since Scarf Victini after a V-Create def + spe drop is easily pursuited, Flare Blitz actually hits slightly harder than Victini's V-Create due to more base atk and Sheer Force and not reducing speed and the defenses may help and Darmanitan also has Superpower to beat Heatran and Tyranitar and Victini only has Brick Break for that and remember that it has less atk and is not using Choice Band so it will be a weak move.
Lastly, Togekiss is a good pokemon and its best set is the stallbreaker you can find
here and even though Thunder Wave may seem more appealing at first since it paralyzes faster pokemon so you can flinch them and with paralyze + flinch it's hard for the opponent to attack, it is hard to fit on its set and Heal Bell helps it support its team and makes it easier to combat bulky teams since it already outspeeds slow walls and it keeps boosting with Nasty Plot and if opposing status appears, it uses Heal Bell to cure that.
Well, i hope i helped and if you need help with the game and want to know which pokemon and sets you should use or just try out premade teams first, check out these links:
Smogdex Viability Rankings Sample Teams