Cool thread. A few weeks ago I wrote an article about marshalling, but it's in dutch :-)
It all comes down to common sense! Marshalls should look at their safety, and try not to interfere with other peoples race.
There is no fixed ruleset, but 90% of the time you can follow a few simple rules that will result in good marshalling.
Here's my article, might translate it at some point! And video's are planned :-)
http://www.rc-offroad.be/bnkinfo-marshall.htm (maybe try google translate
)
In DC's case, the marshall surely had to wait. You shouldn't be punished for someone else making a mistake. At the start of a final for example, if you crash in one of the first corners, you will be be last for sure, as everyone is still driving very closely, so no marshall can interfere.