OnePub allows you to name your private package using a name that is already taken by a public package on pub.dev.
We however generally don't recommend this as it may cause confusion at a later stage if you need to use the same named package from pub.dev.
If you are using the OnePub tools (onepub pub privateonepub pub add <dep>) then there is no issue using existing public names as every package is explicitly referenced with the OnePub URL.
Dart supports configuring your private Package repository by setting an environment variable PUB_HOST_URL.
When you set the PUB_HOST_URL environment variable then every dart pub command will be sent via the OnePub repository.
This has a couple of consequences.
1) OnePub will see every package you depend on. Probably not a big deal, but if you are particularly sensitive about this information then it's not desirable
2) If you use any package name that is already used by a package on pub.dev then you will no longer be able to access the public package of that name. Remember that whilst your package name isn't used today someone may publish a package to pub.dev at a later date.
To avoid these types of name conflicts, we recommend that you prefix your package names with your reverse domain name.