You did weird post. Read it again. Nothing follows from your conversation with dbfx rep, that shows that dbFX and fxcm are the same company. As an IT person you imply, that company is something related to a platform/domain/address/etc.
No, it not at all.
From legal point of view a company is a pile of papers. That's why dbFX rep suggested you to see a contract. That's the only thing that makes sense.
Conclusion abt whitelabeling goes directly from the your point company is something related to a platform
They may accept your application from any partner URL provided that legally they is separate entity. It is not illegal. It is not suspicious.
Take a contract. Check the information abt legal counterparty. That's it.