Yes it is. Duplicati is Open Source, you can build your own version.
It’s also possible to white label the official duplicati package:
The GNU Lesser General Public License allows to use Duplicati commercially and ask money for it, so there’s no need to pay contribution.
Oh… Before I forget: We love money! If you like Duplicati (and maybe earn some money with it), consider a donation:
Great to hear that you want to work with Duplicati commercially. Here is what it says on the Duplicati homepage:
Duplicati is free software and open source. You can use Duplicati for free even for commercial purposes. Source code is licensed under LGPL. Duplicati runs under Windows, Linux, MacOS. It requires .NET 4.5 or Mono.
So I suppose the important part for you is the LGPL (GNU Lesser General Public License) which allows you to use Duplicati code even in proprietary software but with the requirement that the source code must be available. (I am not a lawyer, so you need to check the details with the experts).
Having said that, it would be great if your startup could work with the Duplicati developers in a way that will also benefit the development of duplicati