Can you use FU Abilities during a Counter?

Yes.

Counter gives you an Attack. This Attack counts as a normal Attack for all rule purposes. However, it’s important to remember that you cannot use Abilities when it is not your turn unless the Ability specifically says otherwise. Symbol Abilities specify when they can be used and thus can always be used during a Counter. Disciplines on the other hand might or might not be able to be used depending on their Text Conditions.

Example 1:¬†Since¬†Quick Blow¬†specifies that it can be used during the Follow Up step of your Attack, it can be used during a Counter that occurs on either your turn or another’s.