Often the upload in virtual words is interpreted as a distribute in the EULA’s, and is so not allowed.
The following is an an e-mail communication with Unity. This is to be taken only as an indication. I am not a lawyer. Arises you damage through the use of Unity Assets, I take no responsibility. You must itself assess whether their contents can be used from the Unity Asset Store.
“A question to the EULA please. Can you use asset store contents in virtual 3D worlds like Highfidelity?”
The answer from Ben Stoneman (Unity Technologies):
"Thanks for the e-mail.Yes, you can use asset for any of your projects. It is not allowed to resell the assets as assets.Let me know if you have any further problems.Kind Regards,