I'm fine with hitting on 6+. Compare them to Dwarf Quarrellers (crossbowman) who cost the same points (if the Dwarfs have shields, which is customary).
In their first shooting phase, the Dwarfs may be in range of an enemy unit (both the target and the Quarrellers would have to be far from the board edge). The Dwarfs hit on 5+ with S4. If they are shooting at something with T5+ (a warmachine or giant) they have no hope.
The Chameleons can scout 23.99" from the target and almost certainly get a shot off (in fact, 2 shots, double that of the Quarrellers, WOUNDING on 6+).
They are flexible, pack an annoying punch and are slippery bastards to kill.
I suggest you try them. Take 3 units of 5. And 3 units of 3 Terradons. Concentrate first on recognising areas of the opponents deployment zone that he is ill equiped to kill your harassers. Place them precisely there. Remember that scouting is after all regular deployment (so if there is a gap anywhere, you can exploit it).
If there are minimal weak points, make one. Go straight for that Organ Gun or Black Knight unit that is going to sweep you up and wipe it out with Drop Rocks/poison etc.