The rule in question here is on page 227, and the passage goes:

"Whenever you succeed on a Command Test to issue an order to an NPC who is Devoted or Fanatical (see Dispositions on page 230 in Dark Heresy) you grant a +5 bonus to a single Test related to that order for every degree of success attained."

Now the point of contention is does the Devoted or Fanatical Interaction bonus (+20 or +30) factor into the test, or does it simply allow you to make the test? One seems way powerful than the other.

As I understand it first you test command with +20/+30 modifier for devoted/fanatical. Lets say you ordered a group of pdf troopers to shoot. If you succeed on command test with +20/+30 they get +5 to the BS for every DoS. For example: if you have 55 command you add +20 for devoted = 75. You roll 30. You get 4 degree of success (DoS). Your order was to shoot, so related test is BS. The troopers get +5 to test for DoS = +20. So they shoot with +20 modifier to the BS.