Okay, I think some 5e rules clarification is needed.
1) Polearms are not Finesse Weapons. STR is normally required.
2) Monks have the ability to use DEX instead of STR when they attack with "monk weapons".
You gain the following benefits while you are unarmed or wielding only monk weapons and you aren’t wearing armor or wielding a shield:
You can use Dexterity instead of Strength for the attack and damage rolls of your unarmed strikes and monk weapons.
3) Monk weapons include spears and staves. They do not include Pikes, Halbards and Glaives.
At 1st level, your practice of martial arts gives you mastery of combat styles that use unarmed strikes and monk weapons, which are shortswords and any simple melee weapons that don’t have the two-handed or heavy property.
Conclusion: monks, and anyone with a level of monk who is not wearing armour or using a shield can use DEX instead of STR when attacking with a spear or staff, but not a Pike, Halberd or Glaive.
It should be noted that this does not enable those weapons to be used with Rogue Sneak Attack, which specifically requires the weapon to have the Finesse special property.
