As noted it depends on what oils you are using. That's why I posted the link to clarify that oils can most definitely be electrically conductive.
If you want, check "electrical conductivity of (soy) waxes".
There is also the "breakdown of liquid content/evaporation, etc...".
I was curious, had to have a read up(at least the card will be well preserved ).
Even air and dust are electrically conductive as many PC owners have learned when static electricity zaps their semiconductor components and turns them into junk. Pouring wax, oil or anything else on your mobo is NOT recommended for obvious reasons.
Well the first thing i thought of after reading your post is ' Good thing you didnt start a FIRE' with that Candle otherwise the wax would be the last thing you'd be worried about.
I have seen lots of crap leak through the top of a machine. Putting a candle on the top of a machine is definitely crazy.
Use a large candle plate and next time so not place it on top of the machine.
Be grateful your video card survived