It depends on if the morphs that come with the animation are intended for movement of, say, soft body tissue or if certain body parts in the animation are intended to have a kind of faked collision with those body morph parameters. If this is the case then the animation as purchased will not function properly with your custom character and is intended to be used with the morph settings of the vendor. To adjust the animation to your custom character in terms of body shape would require some or alot of re-keyframing of the animation... 

Caveat, I only do very rudimentary animation projects in Poser usually for props or simple figures that I've made (I find it useful for testing morphs, etc.) So maybe someone here with more experience is aware of a magic wand to wave over your problem...