You have to remember that with EI, you are doing 50% weekly water changes per week to remove any excess amounts and reset the tank that combined with the fact that your plants will continually utilize nitrate to grow assuming all other things are equal - you have a heavily planted tank, your are dosing other required nutrients(the EI method pretty much assures this) your c02 is within appropriate levels, and your lighting is sufficient combined with your c02 level to spur nitrate uptake and growth, you should be fine. From what I understand, even the Father of EI, Tom Barr maintains several tanks with what would be considered high nitrate levels and he has kept fish in those tanks for several years without problems. Getting accurate nitrate level readings is also dependent on ensuring that you are using accurate properly calibrated test kits. It is not a bad idea to test your tap water with such a kit as some tap water can contain significant nitrates. In cases where your tap water is high in phosphates or nitrates you can cut back on the amount that you dose with EI. EI is a highly flexible method and many people successfully adapt it to their particular tap water parameters without problems.
I think that high nitrates only become an issue in non-planted tanks where they don't end up being used and will often build up and remain at consistently high levels, especially when people over feed their fish, don't do water changes, and overstock their tanks full of fish.
One thing that helps soak up nitrates like a sponge is the use of floating plants like egera densa, cardamine lyrata, water lettuce, riccia, etc., So if high nitrates concerns you, having some floating plants to soak up extra nitrates is not a bad idea.