The Wikia notes that weight doesn't affect teammates, so lightweight mods do not provide an advantage to them. In that case, What other mods do not provide benefits to teammates?
Scopes or any Concentration Mod, as Squadmates do not benefit from Accuracy Increase or Weight Reduction. Stabilizers--the ones that decrease weapon spread--however works well on them, as it doesn't affect their ability to aim just the spread of the weapon.
Similarly, Power Magnifiers work well with them but Omniblades and Melee Modules don't effect them because they'll default to shooting someone at any range, very rarely will they engage a melee attempt. Only if an enemy is point blank, and they're in a reload cycle, they'll break their animation and perform a basic attack. Squadmates cannot use Heavy Melee Attacks, so the modifications that increase damage post executing someone with a Heavy Melee Attack also won't benefit a squadmate.
In general, I find that most of the time, sticking mods on squadmates are more or less useless and only for aesthetic value. The exceptions are the most basic ones, such as the barrel mods for increased damage. Piercing barrel mods are hit and miss, as some Squadmates don't need it--as if they have any kinds of special ammunition, they'll always have it on.