Omniplan as well as many of Mac programs (depending on version Numbers, Pages, Keynote, Omnigraffle) are actually not a single file. You can verify this by using the terminal and So that presents a problem for the server. An Omniplan file is actually a folder. So depending on the browser you use the result that is uploaded can be strange. Safari will pull a sort of trick and convert the file to a zip file before it is uploaded. In that case even with the right settings on the jive side the file can appear as a zip but at least it will not end up being a zip of a zip which can be even more confusing.
These properties will stop Jive from compressing but keep what I said above in mind since it sometimes appear as a zip file but that will be Safari putting it into a single zip file automatically. Trying Firefox with the same file will shed some light on the confusing process.
prevent.problematic.contenttypes.for.ie = false
jive.compressionfilter.enabled = false
Example of an Omniplan file output from the terminal:
drwxr-xr-x@ 7 user staff 238 Jun 6 16:11 ProjectPlan.oplx