Heh dont worry about it, keep going and you'll get a fine feature there. How much of an angle will this thing go at? You may still be able to have a dumb waiter, just modifying the design to suit a slanted tube. In fact the only mod you'd need would be to add wheels on one side of the carriage and counterweight, and of course the carriage would be not square..
Fireproofing would mean a fireproof chute and fireproof doors, which arent difficult, and maybe natural fibre rope that doesnt produce nasties in a fire.
Maybe if your carriage is hooked onto the rope it can be unhooked and longer items hauled up on the rope + hook without the carriage.
In fact a dumb waiter system could run at any angle at all, as long as the shaft is straight - and even if it isnt it may still be workable. Why dont you give us more detail about the shaft available.
NT