I do not have a precise answer to your specific question regarding why Isaac's name would be spelled one way or another in any certain documents, but I do have a few comments on your "HAUTOT" theory. I have always been puzzled why the family would add an initial "H" to the name shortly after coming to America. As we all know, the name Otto is very common in Germany as a first name but fairly rare as a surname. In addition the Christian name Isaak is very rare in Germany based on my doing research in German records for several dozen years.
The combination of two unusual names in the "founder" of the [documented] Hutto line does indeed suggest a foreign influence.
In the 1690's large parts of the Pfalz (Palatinate) were depopulated due to ongoing wars. Then in the first decade of the 1700's there was a strong push to entice settlers to the area from other areas, Switzerland in particular. So it is very possible that the Hautot line did go from Normandy to the Pfalz. Another family which married into the Hutto line was of course the Vernadeau (Varnadore etc) family originally of Limousin.
I think you have made a significant contribution with your suggestion.
Now I wish to make a suggestion. I have been collecting materials for some time in the hopes of writing up a history of the early Hutto fanmily, to include all lines if possible. I know the difficulties but if everyone contributes it might be possible.
Please click on the following link to see my writeup so far, realizing that this is a "work in progress", not the final answer. Comments will be appreciated. I would be very glad to have others join in and perhaps form a sort of committee to carry out this project.http://my.stratos.net/~dvagricola/Hutto.htm