There are two differences, taste and texture.
First, texture. Some margarines behave very similarly to butter in a sauce. But others, especially the reduced fat varieties, can contain gums. They tend to separate when heated, and if this happens, your sauce will probably break. This is a good reason to stay away from margarine in cooking and use it as a cold spread only.
Second, taste. The taste is different, and most people find that butter tastes better. Margarine is a substitute which can't quite reach it. Classical recipes are always made with butter, most of them predate the margarine era.
In your case, we can hope that the author tested margarine in the recipe and found that it won't split in that particular process. Or maybe they were lucky to use a margarine brand not prone to splitting. Also, this is a recipe which tries to emulate an existing thing. If Pizza Hut are not using butter in their original recipe, but margarine or vegetable oil, then the margarine will get you closer to the original taste. So, this is a case where margarine and not butter will give you the taste you are after.
You can probably substitute without much trouble, but if the recipe specifies margarine, I'd try the margarine first and only switch to butter if there are problems.