I think that the official word on this is no it isn't. But it has been a house-ruled to be in my group for like 10 years so I say go with what feels right.
As above ... officially it is not, but I House Rule that it is. However, the spell is grease, not oil, so it does not ignite swiftly nor is it particularly hot.
No it isn't. It makes the surface very slick but doesn't actually coat it in anything. In WotC PHB 2 there is a few spells that function like grease but have other extras plugged on as well.
Generally put if a spell doesn't specifically stat something it isn't a part of that spell.