Aside from structural issues of lack of pointers and access to hardware that is typically necessary for operating system design (fortran is too abstract), fortran also had a significant issue with different versions from different manufactures being, well, different. Fortran 66 was the first industry standard version (before fortran 77), but even with these standards there were many other versions out there.
There were also other languages which did offer the necessary access to memory as memory, and hardware, and a bit less abstract. You had PL/I from '64 which was used to write Multix. BCPL and B from '66 and '69 respectively were also used for operating system development. And then there was and C from '72. And one shouldn't forget the MCP for the Burroughs B5000 written in Algol in '61 (compare with Fortran being introduced in '58).
All of those better languages were better choices for operating system design - and were used for various operating systems. They were standardized, cross platform and stable in a time when Fortran wasn't well standardized and programs that ran on IBM might not run on Digital equipment. They also were availabe very shortly after fortran and people started thinking about writing an OS in a language that was no longer seen as slow (compiler technology and optimizations were staring to catch up to hand coded assembly).
So, no. There was no reason to write an operating system in Fortran when there were much better tools available for those who wanted to take it up. As fortran as a systems language isn't recorded in the history while other ones are, and it certainly would have been notable it is probably safe to say that no serious operating system development has been done in Fortran.
From a Fortran 95 handout:
Not being a general-purpose language, there are some things Fortran is very bad at. Anyone trying to write a compiler or operating system in Fortran is probably mad or about to become mad. However the ‘old’ University Library electronic catalogue, which is soon to be replaced, is written in Fortran, even though this is far from the sort of application for which Fortran was designed.