Are tracers bad for your barrel. Possibly.
The standard tracer round is designed not to ignite the tracing compound (usually a form of phosphorus) until it's left the barrel. In which case, there is no more harm to your firearm than with normal ammo.
However.
Older tracer bullets, and ones which have been pulled/reloaded will have a greater tendancy for the tracing element to light earlier due to degradation of the coating over the tracing compound.
IF the tracing element were to light while still in the barrel, obviously some of the phosphorous could be left behind in the barrel too. As such, it might burn a bit...and since phosphorus burns *RATHER* hot, leaving a bit of phosphorus burning inside your barrel is generally bad for the barrel.
How significant a concern is this? Not much really.
It MAY impact the life of your barrel a bit, but really, when the military designs a standard C-7 to have an estimated barrel life of 20,000 rounds...including tracer fire, how many of us will actually come close to even half that number in the lifetime of our firearms?
Solution? Anytime you fire tracer, follow it up with ball ammo to clear the bore out afterwards.
If you note that your reloaded tracers are not lighting up until 75-100 meters downrange, they're working properly. If you note that your tracers are lit right from the muzzle, then you may have a concern.
As for Canola oil, DFK, DFC.
NS