A lot of wineries you have never heard of, and there are hundreds, sell their wine to the big boys and so don't have tours or tasting rooms. However most do. Some have tours that take you throught the process and at the end, have a tasting. I've never heard of a ban of taking photographs, although you can't wander off.
In reality because of the rolling hills, especially in Sonoma County, you can see a hundred different vistas from the backroads which are accessable right off 101.
I don't think they'd want you walking through their vineyards but I doubt that you'd need to.
When you get up here there are lots of winery maps and they will tell you who has tours and who doesn't.
Since Napa valley is really just a small valley, a mile or so wide and 15 miles long it's harder to get great vista shots, if that's what you're after.
In Sonoma the vista shots are available every few miles on the backroads.
Michael