Yes: You can add any elemental state to any enemy based on the rate because it uses a "rate score" system which will determine how fast/easy it is to apply that weakness state. Eg: if an enemy has 1% fire rate, it will apply 100 times slower if using the fire skill skill compared to the default 100%. The default rpg maker elemental system already provides groundwork for multiple elemental effectiveness, weakness and strengths. It does not allow for multi-element skills however so it's a half implementation from the default side.
No: You do not set an enemy as weak towards a specific skill using this plugin nor do elements apply has a boolean weakness (true/false) in this plugin nor does it set a fixed value of weakness based on enemy attack element as such does not natively exist in rpg maker as elements are applied as rates not as boolean type.
Sorry if confusing but what I'm trying to say is that it does not have a yes or no to your specific question. The question implies specific statement in that elements already have a weakness in rpg maker and this is not the case, hence ambiguous answer.