an iksar betrayer  

The Iksar Betrayer IS soloable by a 65 Monk. I did it today. The Iksar Betrayer himself is an easy solo, the problem is fighting him solo without the surrounding mobs adding.
First of all, I had 'kindly' faction in Chardok, which definitely helped. Fighting the Betrayer where it stood, only one other mob would aggro- a reanimated Dragoon; and taking the 2 at once was not possible. Pulling the Betrayer away from the Dragoon didn't work either, as the Ancient Guardian would add, and further down the Watch Captain would add.
The first thing I had to do is solo the Ancient Guardian in his alcove, he is the PH for the bridgekeeper. Nothing added when fighting him, and I didnt have to use any disciplines to kill it. Next I bandaged myself back to full health, Phantom Called the Reanimated Dragoon, and pulled the Iksar betrayer to the bridgekeeper's alcove. There I was able to solo the betrayer without any adds, and an Innerflame and Whirlwind later the Betrayer was dead :0)
With Kindly faction, the live Sarnaks DO NOT add while fighting Betrayer, though undead ones, the bridgekeeper, and the Captain will add. So using the above method worked fine.