Yes, Life Surge does not affect the DoT portion of Phlebotomize or Chaos Thrust.
However, life surge can be used on Chaos Thrust at times to be a DPS increase. (This is due to the CD of Life Surge being 50 seconds, and the natural "DRG rotation" being 60 seconds long.
I will try and show this using timing:
In a normal rotation, your first full thrust comes at the 20 second mark: HT (2.5 sec) -> ID Combo (7.5 sec) -> Phleb (2.5 sec) -> FT Combo (7.5 sec) = 20 seconds. The life surge CD is 50 seconds, so it will come off of CD at the 70 second mark. If you are following your rotation correctly, this will time up exactly with a chaos thrust. Assuming you are behind the target, using Life Surge on this chaos thrust is a DPS increase because you would have to wait another 10 seconds for a Full Thrust to come up again. This builds a pattern, making every 3rd Life Surge optimally used on a Chaos Thrust.
1st Life Surge - 20 seconds - Full Thrust
2nd Life Surge - 70 seconds - Chaos Thrust
3rd Life Surge - 120 seconds - Full Thrust
4th Life Surge - 170 seconds - Full Thrust
5th Life Surge - 220 seconds - Chaos Thrust
6th Life Surge - 270 seconds - Full Thrust
7th Life Surge - 320 seconds - Full Thrust
8th Life Surge - 370 seconds - Chaos Thrust
and so on.
The problem with using life surge on ONLY full thrust, is that the way the rotation works, you will always have to wait 60 seconds to use your Life Surge. So that extra 10 seconds starts to add up over time. This results in getting only 5 Life Surges in a 5 minute time instead of the 6 you could have had in the same time window if you used every 3rd Life Surge on chaos thrust.
Some notes on this:
1) This is only true IF your chaos thrust lands from the rear. If there is any question about where it will land. you are better off waiting for Full Thrust
2) This strategy will not work if your Skill Speed is too high, as it will cause your rotation to reach chaos thrust before your Life Surge is off CD
3) The DPS gain from this is very minimal, by my calculation it is 7.2 potency/minute (.1125 pot/sec), which is a very small amount of DPS