I was wondering if its normal when inside the upper arch denture, can the teeth somewhat be visible?

Yes: This is perfectly normal and depends on the vertical dimension of your mouth and how much room your dentist and the technician had to work with.

Yes: Having upper teeth visible with a denture is fairly common. I assume you saw the wax try-in before having the denture finished.

Can happen: If your gum ridge is large (good thing) the pink base may be thin and so the teeth which are processed to that base, can show thru.

Depends: If the acrylic used has some translucency properties, yes, you would be able to see them. Especially if they are thin (like in patients with very dense, thick bone).