yes definately. If you can stick you hand in the water and still see it, then the fish will see a fly.
Remember that they have had millions of years to adapt to their environment - they will definitely feed in that visibility.
I once fished at eendekuil where the vis was really bad. I was fishing in Shin deep rapids, and could not see a fish in front of me and i was not getting a take.
I got down on my knees and fished from there, and suddenly started getting takes left right and centre! While i was standing the fish could see me but i could not see them. They stayed where they were but did not bite until i got down and they thought i had moved away.