If your planning on creating / editing OMF objects, i.e. walls, doors, etc., I've found it's best to use the very basic vlax-get / vlax-put functions.
(vlax-get wallObject 'height)
(vlax-put wallObject 'height 84)
I've imported type Libraries in the past and one function I wish "vanilla" activeX had was the 'has method. You can check and see if a collection has a certain member - which is nice.
If you create an instance of a collection, i.e. 'wallStyles, it's best to release it as soon as possible (vlax-release-object).
I've had mixed results when working with OMF objects and ActiveX. I tend to stay away from that now.
Oh, and if you use ObjectDBX for importing styles, beware: some additional attributes, such as property data, materials, etc., don't get imported cleanly. If your attempting this I can expand on the problems and some possible fixes if you want.