Spaghetti CAN be sticky (adding oil in the boiling water serves no purpose) and i think that you could use that "tecnique", I wouldn't advise you to tho it thoIs it really the case that spaghetti is al dente if you throw it against a wall and it sticks to it?
Honestly just taste them and decide for yourself, someone likes them fully cooked, others like them more al dente, cooking is nothing but a nutricious way to express yourself!