Thanks for the info on the tanks. I wasn't exactly sure on the tanking mechanics there other than the needed tank swap. As for the DPS, there isn't a distinction between phase 1 and phase 2 you listed. The dots will appear in phase 1 as well.
See proof: http://dulfy.net/wp-content/uploads/...dreadtooth.jpg
I am not convinced that the DoT is random as the DoT appears in combat logs as Ground Spike (Bleeding) and in every single attempt in my log combat logs only appears with Ground Spike (the actual hit). If you look into your combat logs and sort by chronological order, this should be pattern. Note that the DoT appears 1 second before the actual Ground Spike but it is registered that way as the DoT will tick the same time as the Ground Spike hit.
The other thing I noticed is that in phase 2 (past 50%), sometimes it seems like the boss still do Rock Toss as you will get hit by rocks and receive the DoT even without a red circle beneath you. You will see rock toss animation instead with rocks flying at you rather than spikes from under you. The damage, however, still registers as Ground Spike.
Oh another thing I noticed is that back in PTS Rock Heave had a castbar. This castbar was removed on live it seems, which initially lead me to believe that Rock Heave was taken out.