Yes, they are interchangeable. In fact, I use both, depending on my mood. My wife hates me when I consume too much garlic (I like garlic probably too much), so I use even other options when this is the case.
If I am making a saute with yummy veggies and shrimp I love to use a garlic oil, but eating lobster I may opt for the butter. But certainly either of these would be good with either dish ;--)
One more comment. They might not be interchangeable if you are cooking something really hot, as the butter will break. In my case above, I would add some garlic butter to the cooking dish, but wouldn't rely on it for the saute. For low temp stuff, it boils down to preference.