Does Spellblade get proc'd twice with rageblade passive?

No. It will expend the proc on the first hit of it.

Pretty sure it doesn't.

no. here is the thing. rageblade doesn't make on hits proc twice. it makes on hit EFFECTS proc twice. basically effects that are triggered by landing an auto. spellblade is on hit damage triggered by pressing an ability button.

Think of it this way. Rageblade basically makes you auto attack twice instantaneously. So if you auto attacked with the spellblade passive with an auto attack would you be able to do it again with another auto attack without using another ability? The answer is no so it does not proc it twice.

Same way for Vayne's W. If you have 2 stacks on the enemy then you wouldn't proc the %health true damage twice you would just get an extra stack because you are auto attacking to proc the damage and then getting another auto attack to get a stack on them all at the same time.