If it's your own game and assets, that's down to whatever engine licensing deal you have going on.
If it's not your own game and assets, then... no? Absolutely not? Because that's illegal and this shouldn't even be a question.
HammUEr is a tool to help people that are more comfortable working with old BSP-based level editors still use those in UE4 with its mesh-based workflow, that's it.
More explicit version of the terms of use now prominently on the page.