You'd use "pada" with an object that is not a person. You'd use "kepada" with something that is a person or a divinity. This is because of Indonesian's animacy hierarchy. But some people just use "pada" informally for anything.
They do use "Allah" sometimes. Sometimes you can tell whether people are Christian or Muslim by whether they use "Tuhan" or "Allah" to refer to God, but there is a lot of overlap, so it's not a guaranteed litmus test.