As far as the practicalities of boat fires, Psneeld has it correct. Having spent my life in the fire service of a major seaport, I have a good amount of both experience and training in this area. Most (almost all) boat fires are a "protect the exposures" (neighbouring boats, docks, buildings, etc.) situation upon fire department arrival. Stern in or bow in (especially for the boat involved) will not usually make any real difference in that regard.
Depending on the marina facilities, this problem can be exasperated (allowing the fire to continue to develop in size) due to the "setup" time required for the firefighters to actually be "flowing water" to control the situation.
However, in the unlikely event that boat owners are on scene and able to access their boats, then a stern in tie up may make it easier to "get away" from the fire area. In my experience, this is not a likely event, but it could under the right circumstances rarely happen (and only for boats that are not imminently threatened). Usually access to the dock(s) would be restricted by the fire and/or police officials.
Regards,
Tom