Transiting in a Schengen airport with a Romanian visa

My understanding is that you don't need a visa. The reasoning is the following:

• Generally speaking, airside non-Schengen transit in Munich (or other airports with an international transit area) does not require a Schengen visa as long as you don't want to enter the Schengen area.
• As an exception, the citizens from some countries (originally listed in annex IV to the Schengen agreement) do need an “airport transit visa” (ATV), even if they don't want to enter the Schengen area. India is not on that list so this ATV is not required everywhere in the Schengen area but can still be required in specific country. Germany does require Indian citizens to have an ATV so you can't generally transit there without a visa.
• As an exception to the exception, people who would otherwise require an ATV are exempted from the requirement if they have (or return after using) a visa from some non-Schengen countries including the US and, most importantly for this question, Romania (or, in fact, any EU/EEA member).

If you read carefully, all these rules are detailed in the relevant Wikipedia article. The German embassy in London also confirms this. In any case, if that's possible, it's always best to have the airline confirm it as they have to check that you have the right to transit in Germany before allowing you to board the plane in India.