"First of all, I wonder if the shader tree will/can be used in animations, as when you render just one frame with that option ticked. (I always render animations with poser4 for the sake of time). "

there's your problem right there. remove the shaders and yes, the figures will look bad. you can't use them and poser 4, since P4 does not use shaders for 5 and above.. and these figures were made and textured for 5 and above. sorry, but if you want them to look the same with the shader tree you can't use poser 4.