It is advisable to derive the  total fat from more than one source. The appropraiteness of olive oil would also depend on the reason you want to administer a high fat diet in the first instance, however I think, the volume of olive oil you would need to administer or add to the feed would be too high to be feasible. 

Thanks for answering Adejoke! My high fat diet has 20% w/w, and the normolipidic diet has 4% w/w of olive oil, now I need to find out the amount of soybean oil that must be added to these diets!  

Have you considered groundnut cake, it comes as a dry paste with the oil locked inside it, adding too much  oil  (liquid)  may make the feed less compact and less attrative to the animals

That depends on the protocol and the hypothesis to be addressed.

As mentioned already, that depends on the hypothesis to be addressed. It is  common to enrich a diet with a certain proportion of a given oil (in taylored chow or administered by oral gavage) rather than administering a unique oil type in a fat-free chow. In addition to this, it would be convenient to know the exact fatty acid composition of the olive oil batch you are using.