Octopus deploy tells me that I cannot add this since it is not a supported file type. I also tried creating a tar, but do luck. I was able to load a random zip, just not one created by 7zip.
This is a brandnew install of version 3.3.8 x64 on a Windows 2012 server.
Thank you for contacting us. It looks like the problem is that Octopus requires that the package filename to contains the version of the package. For a detailed description of the requirements, please refer to the Supported Packages section of the documentation.
I have tested the following command, and the generated package uploads successfully:
"c:\Program Files\7-Zip\7z.exe" a -tzip acic.2.3.zip *.dll