Correctly wired, it shouldn't matter. Blocking diodes are supposed to prevent any problems - automobile chargers used by people trying to save a buck might blow their systems, but not a properly installed marine grade system. - ArtbyJody writes it up much better than I can - what I can add is hands on.
Summertimes when working on the boat pierside I run the A/C on shore power(after all, why not be comfy) - and the engine at the same time.
I'd hate to have to disconnect my solar panel to run the engine - don't you think that would be a little odd?
I plug a small generator right into my shore power outlet to fire up my 110 only a/c, while underway on the motor, it's two separate systems made separate by folks with electrical engineering creds