That's true (unless the pitch was particularly sharp). But I think most people would find it aesthetically displeasing.
Depending on the style of the rack, one could use a combination of the two. For instance, one of those half-circle type racks could be screwed into the ceiling, while, at the same time, short chains can be run to the same "wall" to level the rack.
My homemade racks use essentially that approach, because they combine pot racks with a flat shelf whose far edge needed support. So the chains attach to the leading edges, and angle back to the wall.
Not the most flattering photo, unfortunately. This is a beautiful "antique hammered copper pot rack". It's actually copper plated steel, but unless I tell, no one knows, and I believe it's a lot stronger than the more expensive 100% copper ones. It's been in place, and used constantly for the past 4 years, and is just as beautiful today as when it was put up. Don't let the price fool you! There was no support in the place we wanted to hang it. HubbyDearest is clever though, and installed 2"X4"X 6' oak braces across the ceiling, screwing them to the beams with heavy-duty screws, so the rack could be centered in the right spot. There's probably 100+ pounds of pots, pans and assorted other equipment hanging there, with no problems at all. My ceiling is also slanted, but the chains allowed us to hang it level, and it looks great! When I finally ever do figure out how to do photos in my posts, I'll put up a picture of it!
Then a pair of fairly heavy, threaded eye-bolts. Run each into a roof rafter (I assume that's what is above your ceiling) so you're got a solid attachment. Then you're set to pick a rack and get your chains.
You do NOT want to attach your rack to ceiling drywall, even if you use toggle bolts. If the drywall gives way under the load, you could have a big headache.
I found a nice rack with sliding hooks at Containers and Things; they also have packages of additional hooks. My hardware and hooks match the brushed-nickel motif of the kitchen. They have other finishes.
The rails of the rack are wood, and it comes with eight hooks. I made new rails, about twice as long as the original, finished them to match my cabinets, used all the hardware, and have 16 pots/pans (mostly cast iron) hung above the aisle in our small galley kitchen.
Works fine for my wife and me, but if you're taller than 5"-11" you have to be very alert to work in our kitchen!
Unfortunately this includes both our sons, our son-in-law, and many guests. Hey, when you fit a gourmand's custom-made kitchen into an 8' x 13' space, you have to make some hard choices.
Ideally, the rafters will be located exactly where you want to put the eye-hooks to have the rack in the location you choose. How fortunate if that is so! In my case we needed to position the rack over one countertop, centered in front of the window. But the ceiling trusses weren't in the right place for this. HubbyDearest "bridged" the trusses with 2 nicely finished, sturdy oak boards, and fastened them into the beams with substantial screws. The way he put them up gives the appearance of everything being perfectly centered, but the hooks holding the chains are screwed into the oak boards. They actually bridge 3 ceiling beams. The result is that the rack is perfectly centered in the place we needed it to be, with no likelihood of it falling down (unless a gorilla were to swing from it maybe...but we don't let him out of the cellar). :look: