CBD Oil does not have any affect on the BG levels, but with consistent use has a positive affect on pain. I say "constant use" as it does need to build up over time. Unlike typical pain medications that take affect usually within an hour, CBD Oil action on pain is not noticed so quickly. When you do notice is when you stop taking it and the intensity of pain returns.
That said, CBD Oil with THC content (like a 1:1 blend) has a more noticeable affect on pain and sedation but takes up to 4 hours to be absorbed and work. Caution, though, as THC affects people in different ways. The THC affect is for about 12 hours so no driving, no work that requires safety, and it will give you the munchies - and that will negatively affect your BG levels. If using CBD Oil with THC then plan to have Diabetes-friendly snacks available when the munchies crave hits and it will.
Again, CBD Oil by itself, or with THC, does not affect your BG levels. Since legalization in many places, a lot of research is still needed to study the various strains of marijuana, and its derivatives, as it has helped people with various ailments and inflictions (but not Diabetes).
I use CBD OIL during the day and occasionally CBD Oil with THC in the evening to help with my sleep (does that very well). Just remember the 12 hour rule if using with THC content. You could be caught driving impaired the next morning if taken too late at night.
BTW, you cannot overdose with plain CBD Oil, but be careful with the level of THC if using a CBD/THC blend as the psychoactive affect (known as a "high") increases with higher levels of THC.