Grammatically, yes, it is natural. In terms of vocabulary choice, I don't know anyone who ever says 'scrumptious,' unless they want to make a joke/be sarcastic about it. Use "delicious" instead. 'Scrumptious' sounds like a word only old ladies would use. But if you're an old lady already, sure, you can say it.

I agree with the other answers. There's no need to say 'taste' because taste is implied in the adjective. We don't really use the word 'scrumptious', though. It sounds like something from the 1930s. Like Brian, I have never heard anybody use it unless they were joking. In fact, I've never even heard an old ladies say it. I wouldn't use it, if I were you.

I would say, "This cake is scrumptious." To me, the word "scrumptious" already implies taste so 'taste' can be left out.