The inverted engine did pose problems with oil supply and consumption. The British sent a team to Germany immediately after WW2 to investigate the German engines and speak to German engineers. The British team comprised men from the Ministry of Aircrat Production and all the British aero engine manufacturers (including Armstrong Siddeley Motors, Bristol Aero Co., D. Napier & Son and of course Rolls Royce). They produced a report, 'Comments on Visit to Germany, July 24th 1945 to August 12th 1945'. In it they recorded that Daimler Benz engineers would have preferred an upright 'V', but the inverted layout was a requirement of the RLM (actually it predated the RLM, back to 1928).
They made the point that it was very difficult to get even oil consumption as the rotation of the crankshaft caused one bank to get more oil than the other. It's why the compression ratio is lower on one bank than the other.
Cheers
Steve
Edit: Quote from report:
"With the inverted engine, they said it was very difficult to obtain consistent oil consumption and due to the rotation of the crankshaft one cylinder bank got more oil (spray) than the other. This oil got past the pistons into the combustion chambers and reduced the anti-knock value of the charge. For this reason the engine was built with a lower cylinder compression ratio on this bank than on the other."