Can you pick a unit while off the table for Battle tactics?

[Maddpainting]

Looking over the Flagellants new WD Battle tactic it got me thinking and I could not find it anywhere (though I could be over looking it or looking in wrong spots). 

Can you choose a unit that is off the table to complete a Battle Tactic? 

The only rules I found were

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3.1 Units cannot cast spells or use abilities while they are in reserve unless the spell or ability specifically says it can be used by reserve units.

And looking up what an ability is 

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22.4 ABILITIES
Most warscrolls include one or more abilities (see 1.6). You must use the rules on a unit’s warscroll if the unit is part of your army. The abilities section will also include information about any command abilities or magic the unit can use.

So I see no reason why I can not, but it feels like you should not be able to. 

[Liquidsteel]

I think you can, yes. 

Reason I say that is one of the ghb missions has you select 3 predator units to use for extra points scoring, and it specifically says they have to have been deployed on the table.