I'll keep an eye out for the McIntyre name, however my files concern the loyalist era, and your Joseph would be in a later generation.
Forgive me if I review things you know all too well. Because your multiple-great grandfather was born in 1794, he would not be a loyalist (they arrived in New Brunswick in 1783), but he could be the child of a loyalist. The family story may have confused him with his loyalist father when it recounts that he got land from the queen and king. Someone born in 1794 would not have been able to fight with the British between 1775-1783 (the years of the American Revolution) or even during the War of 1812. African-Americans were given their freedom if they fled their masters in 1812 and served the British. Joseph would only have been 8 for that war.
Is Elm Hill along the St. John River or is along the Bay of Fundy coast? My family hails from Saint John and I graduated from Moncton High, but the name Elm Hill is new to me.
As I said, I will keep an eye out for the McIntyre name.