The original iPad only supports the A2DP (music streaming) profile. This means that you can use any Plantronics headset that includes A2DP to listen to music or podcasts on the iPad, but you cannot transmit audio.
Plantronics headsets that include the A2DP profile are:
iPad 2 and Newer
The iPad 2 supports the A2DP and HFP profiles, so you can use any Plantronics Bluetooth headset to both listen to and transmit audio.
Note: The ability to stream music on the iPad through a Plantronics headset is also dependent upon the music player itself. Certain apps do not support streaming to a headset even though the iPad itself supports it.