We don't do live-fire training on houses with hoarder issues, it's too dangerous for the firefighters. Considerable chance of entrapment/entanglement. I'm prepping a house right now to use for training this fall, and we're removing all the junk first, and it was mostly-empty to begin with.
Also consider that firefighters will be quite hesitant to perform a search of the home if it is burning for real if it has a hoarding problem....