I would doubt you would get enough radiant heat off the unit to heat the garage unless the garage was well insulated and fairly airtight. But then the smoke could not escape very well. If you are getting that much radiant heat then the owb needs to be better insulated. The only area on my Central Boiler that would give off any heat is the outer area of the door that is not insulated.
As far as having a dry place to load, it would be nice but once I have the wood in the wheelbarrow I am only actually loading for a minute or 2 twice a day. I am already dressed for the weather so it is a non issue for me. Again, just my opinion, this is my 10th season with the owb and I have been the only one loading it except for a very few times.