This is generally handled by having all parents in USD in the main hierarchy. This way, the base entities are translated to USD - they take into consideration all USD overrides. Then alternate hierarchies are used to view parents in other currencies.
Unless I'm not understanding the question correctly, there is a field called Auto Translation Currencies in the entity dimension. You could have an EUR entity tree to an EUR parent, but put USD in the Auto Translation Currencies field. Of course if you are using dollar overrides in the equity section, this could potentially get complicated, but you can test for the currency member in rules.
Be aware that Auto Translation Currencies does not consolidate (and also adds time to your consolidation). So if you look at your immediate EUR parent in USD, it will translate the parent values to USD rather than consolidating the USD amounts from the children.
That's correct. It's definitely flawed. But it's also useful, especially if it avoids having to maintain (and consolidate) two different structures. As in all implementations, there are multiple approaches with multiple pros and cons.
