Hi!
Jumping in on an existing discussion here instead of creating a new one; I updated to VMWare Fusion 7 yesterday, and are having this exact same issue getting Unity mode to work. Checking my logs, I see this:
2014-10-21T08:45:51.143+01:00| VMware Fusion| I120: IsTopologySupported: Guest screen size limit: 8192x8192, 2 displays max, bounding box memory limit: 67108864 bytes.
2014-10-21T08:45:51.143+01:00| VMware Fusion| I120: IsTopologySupported: The topology has 4 monitors, which exceeds the current limit of 2 monitors. Returning false and setting powerOffNeeded = true
When attempting to go into fullscreen, I get a mirrored configuration on all my displays - and Windows only sees one screen. In addition the resolution is way off, so in addition everything looks horrendous.
My topology consists of the laptop screen (MBP Retina), two 24" screens and one 21" screen in non-mirrored mode. This used to work just fine in VMWare Fusion 6, and after updating I'm forced into doing my Windows-work (which is a big chunk of my workday) inside a single window on a single desktop. Having a limit of two monitors supported in a topology seems mindblowing, I hope there are imminent plans to increase this? Having two external monitors hooked up to a laptop cannot be a weird use-case, there are three display ports on a MBP. I really hope there is a quick solution to this, because at the moment I'm regretting the upgrade.