Yes, if you want to use the same NIF, but a different button, you need a new Art Define. If I am understanding your question properly.
Actually, it is a bit more complicated
I have in TEARS_CIV4ArtDefines_Unit.xml :
ART1 : NIF1, BUTTON1
ART2 : NIF2, BUTTON2
ART3 : NIF3, BUTTON3
And in TEARS_CIV4UnitInfos.xml :
UNIT1 : ART1, ART1, ART2, ART2, ART3 => BUTTON1 (?)
UNIT2 : ART1, ART2, ART2, ART2, ART2 => BUTTON1 (again!)
UNIT3 : ART2, ART2 => BUTTON2
UNIT4 : ART2, ART2, ART2, ART3, ART3 => BUTTON2 (again!)
UNIT5 : ART3 => BUTTON3
You see my problem ?
I do not find it logical that the button is not defined in the UNIT Xml instead of the ART Xml, this way:
ART1 : NIF1
ART2 : NIF2
ART3 : NIF3
UNIT1 : ART1, ART1, ART2, ART2, ART3, BUTTON1
UNIT2 : ART1, ART2, ART2, ART2, ART2, BUTTON2
UNIT3 : ART2, ART2, BUTTON3
UNIT4 : ART2, ART2, ART2, ART3, ART3, BUTTON4
UNIT5 : ART3, BUTTON5