Anglers as you probably know have huge mouths and can swallow really big stuff. A baby octo certainly wouldn't be safe. But on the other hand, if you get a large octo, the tables are turned and the angler isn't going to be too happy. They also might compete for food if you feed the angler shrimps.
It depends on the exact size, an octo can take on something 1 1/2 times its mantle length and even venomous fish. Sorry to be so negative but octopuses simply don't do well with other fish in aquariums.
I think all combinations of predatory animals are a matter of luck.
you can always try, if you're lucky, you'll have a feature, if not, well you gave it a shot
e.g. I once was able to keep 3-5 cm apistogramma ramirezi (a small cichlid) with a 50 cm arowana (big predator with a huge mouth). it went great. the aro I've got now even takes out 20cm fish if they bother him too much.