Bestigors Despoilers question

[Tibus367]

The bestigor's despoilers ability says "Add 1 to hit roles for attacks made by this unit that target enemy units with 10 or more models.  In addition, you can re-roll hit rolls of 1 for attacks by this unit that target Order units"

If I add 1 to a hit roll then it is impossible to roll a 1.  Does that mean that I can not add a +1 to hit against Order units that have 10 or more models (just re-rolling 1's).  Or is the intent that I can re-roll 'unmodified' rolls of 1 in this case.

[Skreech Verminking]

Modifiers are added after the reroll meaning, the +1 to the hit role will be added after you rerolled  the one you would have rolled 

edit: you can look the rules up in the core rules at page 12 by modifiers

[King Taloren]

Also 1s are failures regardless of modifiers so yes you still roll 1s to reroll.