The vacuum nipple thing is on the throttle body. I managed to remove the little rubber cover and fit the tube to the scottoiler without removing the tank, but it was VERY fiddly and I scratched my hands up quite a bit squeezing them through the gaps! If I were doing it again, I'd take the tank off for sure.
The back wheel does get oil flung on it a fair bit, but I tend to run the oiler set to drip a bit more out than recommended since I ride in all weathers. I'd rather have a dirty back wheel than a knackered chain & sprockets though, much easier to clean a wheel! I find a quick brush with paraffin followed by a squirt of muc-off followed by a rinse with the hosepipe soon cleans the wheel up.