Why does the vav before 'men' sound like an 'o' instead of a 'v'? I've noticed this whenever "and men" is referenced
The "and" ו turns from "ve" sound to "oo" in a few occasions. One of them, here, where the word starts without a vowel - גברים = gvarim - the g goes right into the v, no additional vowel. To eliminate consecutive non-sounding (or nearly so) consonants the language turns the "ve" into "oo"
I'm no expert in such rules of the language, but just wanted to note that in a casual manner of speaking you can pretty much always say 've' and it would be perfectly acceptable..
(which is possibly a mistake but nowadays that's how people in Israel speak...)
So just to be clear, when it comes to "and" the 'o' version is common in colloquial Hebrew, sounds more natural, but is viewed as incorrect traditionally? When can it occur? Before consonant clusters?
The 've' version is more common in colloquial Hebrew. There's no 'o' version but rather an 'oo' version, (meaning it sound more like an 'u' sound). It's not very common in everyday talk.
So it's like oog b'v' reem? It's so fast it's hard to hear without knowing what it SHOULD be :-)
If you read something in Hebrew and there is a vav with the dot on top it makes the O sound. If there is a vav and the dot is in the middle of the vav, then it makes the oo sound. Some remember it by the dot being a fist and the vav being a person. If I punched you over your head, you'd say "OH! That was close!", but if I punched you in the stomach, you'd say, "OO that hurt!!"
Nice example! Are there any rules for when Hebrew is not being written with niqqud? E.g. for the Tips & Notes for Letters 2 it has this useful tip for deciding when to pronounce bet as 'b' or 'v': "In writing without nikud, a letter without a dot could have either pronunciation, but its position in the syllable will help you guess the right pronunciation" (they then give examples).
No rules, just practice and recognize. The reason being that the ב being b/v - is purely grammatical, so it stands to rules. Here, the ו has two separate roles, as a consonant, or as a letter implying a vowel. It's just memorizing word spelling.
We get that, but we want to know why in this context it's not pronounced like "v" but rather "o."
most people don't know when to use oo, so they just use ve, or quite commonly use oo incorrectly