Hi Carol - I am related to the younger brother (George) of your Isaac H Daniell. Interestingly, my George's 2nd oldest son is named Isaac Hill Daniell. (His oldest son is named William, after their father.)
So, although I can't say for sure the "H" in his name is "Hill," it's quite possibly he could be named after your Isaac since that was the brother nearest to him in age (they were born just two years apart 1781 & 1783). Just thought I would mention, in case that is helpful to you.