I’ve certainly heard that as well, though not so common. My homeland straddles the border of Durham and North Yorkshire and some of my relatives who live high in the dales pronounce “book” almost like “bowk”
Are you sure people in the southeast rhyme “blood” and “flood” with those other words? I mean, you would know better than I, as I’ve lived my whole life in the southwest (plus 4 years in Nottingham for uni), but I’ve mixed with people from all over and it definitely sounds ‘northern’ to my ears. For example, imagine the phrase “bloody hell” in an Essex accent and a Yorkshire accent - clearly different, right? And yet I would say in Yorkshire, “blood” probably does rhyme with “good” for most people, but I wouldn’t say the same in Essex - I feel the “good” pronunciation is common to both accents, but (as per the OP) in the south, very generally, “blood” has the “u” sound from “butt”. It certainly does for me.
Okay, can we just stick to RP/ Queen’s English/Oxford English, and use the IPA phonetic transcription listed in an English dictionary. The sound should be transcribed as ^.
I don’t know if there is a real answer. I have only hearsay that any exists. I hope it isn’t another -gry question, but it might be.
South Hampshire here; in my dialect:
Good rhymes with would, should, could - ʊ
Blood, flood do not rhyme with any of the above - ʌ
Blood:
I’m not saying my way is right and the others are wrong, but this is just how it is spoken here
What he said.
(Except herts instead of hants)
Not that I know of, as a born-and-bred Chicagoan. We do have more than one accent here in Chicago, but none of them pronounce “crook” and “foot” as “cruk.” We do sometimes say “roof” with the same vowel as in “book” (and “crook” and “foot.”) “Crook,” “book,” and “foot,” all have a /ʊ/ sound in my dialect. “Roof” can be /ʊ/ or /u:/. I think the former is more predominant among people who grew up here.
That’s fooked up. 
My point was more that “good” seems to be only pronounced in one way. Certainly for some accents it is different and it doesn’t use the same vowel sound as “blood, should, would, could, flood etc” so on reflection “universal” was the wrong word to use, “widespread enough to be considered a standard pronunciation” is probably more accurate.
I agree with you on “good”. But I’m still not clear: are you saying “blood”, “should”, “would”, “could” and “flood” all have the same vowel sound for most English speakers? They certainly don’t for me, and I suspect they don’t for most brought up south of Watford. But I also think I don’t have a great ear for this sort of thing, so I could be wrong.
I wouldn’t stick my neck out and say “most” but certainly for enough of the country that it can be considered “standard pronunciation” if indeed anything can be considered “standard pronunciation” (I personally think English, as spoken in the UK is too fragmented to lend itself to such an easy classification)
We are talking about a complex set of vowels here, and I think it might be useful to go into some detail.
When talking on broad terms, say General American, and Received Pronunciation, we can talk about these vowels:
[ʌ] call it the cut vowel – note that there is significant variation in this vowel–a Conservative R.P. speaker like Hugh Grant has a noticeably tighter and higher “cut” vowel than a General American speaker
[ɔ] – the “caught” vowel
[ɑ] – the “cot” vowel (in General American)
[ɒ] == the “cot” vowel (in R.P.)
[u] – the “coot” vowel
[ʊ] – the “foot” vowel
In a lot of American accents, “cot” and “caught” are merged
In some American accents, “cut” and “cot” are merged, so, for example, “gulf” and “golf” are pronounced identically
In a lot of Northern England accents, “cut” and “foot” are merged
In a lot of Southern Scotland accents, “coot” and “foot” are merged, so, for examole “full” and “fool” are pronounced identically.
Do we know where the OP on the other board is from?
No, unknown. And the thread has been deleted.