Yes. It'll work fine. Modern NIC cards auto sense the Tx/Rx pairs. No switch needed if its just two hosts.
Each host will assign itself a 169.254.x.x address. They will then be able to see each other via mDNS. (This is the same thing that happens with IP-over-FireWire). The two systems form a 2 host point to point LAN connection between them.
.....This is all assuming you can find a 10Gbps NIC card that works in a MacPro.
- CK.