I would expand that to say they are not DIRECTLY impacted by the price of oil, but there most certainly is a lot of indirect impacts.

First and foremost the price (and therefore supply/demand) of oil has a major effect on where in the world oil is being produced.  This is a very obvious factor in this case: If the price of oil is low no one wants to invest in the expensive oil production we have in the Canadian oil sands, therefore it doesn't make much sense to expand pipelines to carry oil out of the oil sands, there just won't be the oil to transport!

On the flip side some pipelines will benefit from LOWER prices as that raises demand and therefore they'll be transporting more.