I just finished successfully installing open-vm-tools in a FreeNAS 7.2 guest running on ESXi 4.1. I used the notes on BlackStudio.com as a reference. Those notes were more or less accurate but I did have to start over twice due to poor assumptions on my part (size of OS partition, etc.).
In any case, I can now start/stop the FreeNAS server via the ESXi console. Notes in the wiki shortly (I have a backlog, don't I?).
Update: I've received a couple requests for the packages (one from v1ncen7 below). The howto is here. The link for a tarball of the generated packages is at the bottom of that page and here. The usual disclaimers apply (i.e., your mileage will vary).