It's his default armor, early on there was a bug that his armor looked like republic armor. They have since fixed the issue and now he shows in his typical sithy gear.
If you plan on solely playing the role of DPS, go with sentinel as it is superior in both PVP and PVE. If you ever have aspirations of tanking go Guardian.
Three sets of gear for the roles I play.... (4th set stored on Scourge)
Tank :
http://cloud-2.steampowered.com/ugc/596988571317357083/F1B1DA6B8BC26C6464104D6C8A84CB48DC5AE812/
http://cloud-2.steampowered.com/ugc/596988571312084449/0E8E19C7C525BF3AEDFC25D749CE0A37D1EC8531/
PVP :
http://cloud-2.steampowered.com/ugc/596988571312092206/C717E5A71283A4C6560AF6E0D835ECC2FD567BD5/
http://cloud-2.steampowered.com/ugc/596988571317530694/6B1C40B801BB19DCFF53F9E574AFFC23241B23DD/
DPS (work in progress) :
http://cloud.steampowered.com/ugc/596988571312087948/A01322942FDEADFA346B88A169997BC57396F3DA/
http://cloud-2.steampowered.com/ugc/596988571317366086/93E5E41F16492D92BCFC8CC59747B425B7C12D38/
Completed as a pvp tank spec (27/12/2) back in Jan on my 1st try so it is possible. I thought the fight was more difficult than it would have been on a DPS but very fun and very doable. Changing it would only diminish the epicness of fighting the mofo'in emperor!
I find you spec to be situationally effective. If you are running in a group with x2 shield spec vanguards and a tanking shadow another tank is not helpful. But if you are in fact the only tank in a group this and the 18/23/0 spec would be very effective. Now both of you quit your bickering.