Lenovo Thinkserver TS140 supported by Proxmox?

Provided you get this: ThinkServer RAID 700 II Adapter (6GB SAS/SATA HW RAID 0/1/5/10/50) with Battery Backup
The other raid options mentioned is fake raid alias software raid which is not supported.
The ThinkServer RAID 700 II Adapter is equipped with LSI SAS2108 which is supported throughout proxmox 3.x due to the RHEL 6.x kernel. The same applies to the coming RHEL 7.x kernel.