The spell helps with the damage but not the saving throw.
The spell protection from poison gives the following benefits when cast on you:
For the duration, [you have] advantage on saving throws against being poisoned, and [you have] resistance to poison damage.
The armor you are trying to wear does not poison you; it deals poison damage to you. This is an annoyance of terminology in 5e: there is a condition called "poisoned" and there is "poison damage." The two often show up together but they are distinct, because one is a condition and one is a damage type. If you pretend they were called the "sickened" condition and "toxic damage" the disparity might be a little more clear.
Since the armor is not trying to poison you (it can't give you the poisoned condition), you are not making a saving throw against being poisoned. You are making a saving throw against taking damage that happens to be of type poison. You do not have advantage on the saving throw.
However, whether you succeed and take half damage (about 50) or fail and take full damage (about 100) from the armor's curse, that amount of poison damage is then reduced by half (to about 25 or about 50, respectively). You do have resistance to the poison damage.
So, yes, you would be benefited by using that spell before putting on the armor, but only with the damage resistance, not with the saving throw.