Does Freebsd 9 support Z68 chipset like in Intel DZ68BC motherboard? Will I have any "unrecognized device" issues ? What about Freebsd 8? What's the best way to find it out ?
There is nothing, that is not working with a motherboard as the one you list. Even Sandy Bridge Integrated Graphics are more or less working by now, which has been an issue for a while.
Since motherboards generally just provide generic I/O stuff there are usually no specific drivers required for their basic functionality is supported by generic drivers.
Additional SATA Controllers sometimes tend to be rather esoteric and may require additional drivers. For (normal onboard) Sound devices and Networking on the other hand the available chipset choices on the market have become so small by now that you'd probably have trouble finding an unsupported device.