Raw garlic in Sunflower oil

I agree that they're similar, but I don't think I'd personally call them "interchangeable" in a culinary sense, just like butter and oil aren't really interchangeable in all cases.

Now, it's not like the ingredients police will arrest you for using one in a recipe instead of another. Note that melted butter is about 20% water (depending on how long you've heated it), but you're probably not baking with this stuff (though it occurs to me that it'd be an interesting addition to a salty cracker recipe).

The most common data point seems to be that any moisture level below 35% will inhibit growth of the C. Botulinum spores that cause botulism. It's hard to point to true scientific sources because they tend to be protected, but if you spend a few minutes on Google (try this query) you'll see that it is in fact confirmed in several of the scientific journals.

I seem to be seeing snippets of references (which I can't view the full text of) that suggest possible growth at moisture levels as low as 16%, but most garlic flakes have 6% moisture or lower, which is way too low for botulism.

If you are seriously concerned - perhaps you live in a very humid climate and don't have air conditioning - then toss a desiccant into the container to be sure that the moisture level stays down. The most popular are those little packets of silica gel (don't open them!), but there are many more - see Wikipedia's list of desiccants.

Honestly though, chances are your flaked garlic is already free of C. Botulinum spores after the dehydrating process, and nothing's going to grow no matter how you store the dried stuff. The above paragraph is only included for the hyper-paranoid. Powdered/flaked garlic is safe to store at room temperature.

If you're actually storing this garlic in the oil (it's not entirely clear from your question) then that's another story, and theoretically you're making it possible for the spores to grow again. So it comes down to a question of whether or not the garlic flakes are already clean. That's extremely likely to be the case, but not a sure thing, and personally, I don't know if I'd chance it; best to follow the same precautions as those for fresh garlic and soak them in vinegar for 24 hours to kill any spores (although you might as well use fresh garlic in this case).