The phrase "allowed to exist in" is correct and usable in written English.
It can be used when discussing permissions or conditions under which something can be present or maintained in a particular context or environment.
Example: "In this ecosystem, certain species are allowed to exist in harmony with one another."
Alternatives: "permitted to be in" or "authorized to remain in".
The caliphate has survived its first year of existence, and as long as it is allowed to exist in Syria, it will continue to expand, both there and abroad.
In Eastern Europe, their leaders target the Roma "who shouldn't be allowed to exist", in the words of one.
Critics have asked whether these all-male, unelected village councils should be allowed to exist in modern India.
-- Janusz Kaminski "I'm fascinated by movies made in the 70's and by the reality that was allowed to exist in front of the camera.
Rival political parties are allowed to exist in both areas, but with no region-wide elections since 1992, they have scant opportunity to prove themselves.
Nothing was working except the artists' associations, the small businesses, the hiking clubs, the student groups, and the networks of friends that are barely allowed to exist in Burma.
There is nothing showy, nothing overstated; the pictures, like the girls, are allowed to exist quietly in their space.
It means that several encrypted versions of a plaintext image are allowed to exist simultaneously in the proposed scheme, which not affects the normal operation of the proposed scheme.
As long as too-big-to-fail banks are allowed to exist, they will be in a position to extort the government and the taxpayer in a crisis.
Peter Mandelson was allowed to exist for years in his own world of pantomime morality, yachts and Russians buzzing round him like flies while we all just laughed it off.
It was Niantic's first game — and while it never became the overwhelmingly popular phenomenon that GO did, it's undeniably what allowed GO to exist in the first place.
