I have found a dll that is provided via Google Code and I couldn't find it in NuGet. I want this package to be available via a NuGet install, because I want to reuse it in several packages and NuGet seems like the perfect way to do this.
https://code.google.com/p/protobuf-remote/downloads/list
Is it possible for me to generate a nupkg out of these dll's and publish it to NuGet.org? What are the legal limitations to this action?
There are a number of other users that have run into this issue. It seems like the common solution is to create an "Unofficial" package and reference that for the time being (until Google publishes their library as a NuGet). Just make sure to very clearly label the package as unofficial. See these examples.
As for the legal ramifications...
Please look through protobuf-remote license and review the distribution and derived works details. Currently the license is GNU Lesser GPL. Sorry, but you'll have to make your own call on if publishing the NuGet package would be permitted under this license. ;)