To answer your question, yes the dots from Serpent Sting and Immolation/Explosive Trap stack just like Nazeebo's trait and Huge Toads' dots stack. Baseline Serpent Sting do not stack by application though but it can through the lvl 16 talent Wyvern Sting. As for the numbers, as I've mentioned in the disclaimer, I haven't decided the correct values yet, and numbers should be ignored for now. Numbers were just here as placeholders from other similar abilities.