Some creatures use the original animations because those creatures animations haven't changed since the original game.
I guess you could copy over an original player animation and have them use the original weapon/armour animations that remain in
BG2. Unfortunately I think only certain helms, shields and possibly some weapons remain from with the original
BG1 animation.
For example, you want to copy over a cleric; so you give him a
BG1 helm, but can't find a weapon for clerics carried over from
BG1 and there is no armour for
BG1 animations in
BG2...so your animation won't be wearing armour.
If you gave the
BG1 animation
BG2 armour it would probably crash your game or else the armour would look like it is floating above or to the left/right of the creatures body.
The other thing with copying over an original
BG1 player animation is that you would have to use up an existing animation slot or one of the free ones...see the thread hereabouts on porting
PST animations to
BG2 for info.
A knight without armour in a savage land...