your dry hops won't be affected. it's really all about the amount of bitterness you get out of the hops, so really only the hops that get boiled for a long time.
also note that the gravity does not even make a major impact on the hop utilization unless the gravity is significantly raised.
example:
5 gallons of 1.050 wort with 1 oz of a 10% hop boiled for 60 minutes will get about 45 IBUs.
If you up the gravity to 1.060 (which is a pretty big difference) and keep the hops the same, then you get only (gasp!) 42.5 IBUs.
45-42.5 = 2.5 IBU lost due to a 10 point gravity difference. that's not much difference.
it's more important for people who do the 3 gallon thick wort boils.
another example:
end product is going to be 5 gallons of 1.050 wort.
it is cooked as 3 gallons of thicker wort with a gravity of 1.083 (that's a MASSIVE difference from 1.050)
that 1oz of hops will end up giving you only 38 IBUs after you dilute the 3 gallons of cooked wort to 5 gallons.
so, now we're talking about a bigger difference. 45 IBU vs 38 IBU.