You would need to add it as a Raw Device Mapping to a virtual machine, in order to be able to use the previously formatted partition. Adding it to a host will format it.
Brian Atkinson | vExpert | VMTN Moderator | Author of "VCP5-DCV VMware Certified Professional-Data Center Virtualization on vSphere 5.5 Study Guide: VCP-550" | @vmroyale | http://vmroyale.com