I have never used the Grabber 2 bike rack, but it will be safe to use it to carry 2 bikes on your (1998-2002) Honda Accord.
Generally, car bumpers are made up of 2 parts: a metal bumper, and a bumper cover.
The metal bumper is the part that will take the impact if someone hits you from behind. The metal bumper for a 1998-2002 Accord is shown below.
On top of the metal bumper, there is a plastic bumper cover. Its only purpose is to make the car look nice. Your Grabber 2 rack will probably be resting on the bumper cover when you install it.
I highlighted the points where your rack will probably rest on the black 1998-2002 Accord bumper cover, shown below.
Below is a picture of a 1998-2002 Accord, with the same points highlighted.
You might notice the plastic bumper cover flex a little when you load the bikes, but this is nothing to worry about. The plastic they use for bumper covers is meant to take small impacts without cracking, so having the weight of 2 bikes resting on it will do no harm.