Distinguishing /f–t–θ/ in th-fronting and th-stopping dialects

In standard English, the digraph th is a dental fricative [θ, ð]. Several dialects feature th-fronting, where th becomes a labiodental fricative [f, v]; others feature th-stopping, where th becomes a dental stop [t̪, d̪]. For example, three sounds like free with th-fronting, tree with th-stopping.

How well can English speakers distinguish word pairs in these dialects? Specifically:

• Can th-modifying speakers distinguish /f–θ/ and /t–θ/ in their own dialects?
• Can they distinguish minimal pairs as spoken in standard English?
• Can standard English speakers distinguish the th-modified variants from similar words?

I expect that the answers vary between dialects and individuals, so I'm interested in reasonable generalizations. If there's a significant difference between (for example) th-fronting in Cockney and African American Vernacular English, I'd be interested in that too. Likewise if there's a significant difference between the voiced and unvoiced consonants.

Wikipedia notes that th-stopping dialects generally distinguish between the dental stop of thanks [t̪æŋks] and the alveolar stop of tanks [tæŋks], but they lose the /t–θ/ opposition in some cases like tree/three, and the /d–ð/ opposition is even weaker. This answers part of the question for th-stopping dialects: They can sometimes (but not not always) distinguish /t–θ/ in their own dialect, and I imagine they can also hear the opposition in standard English. I'm not sure whether a typical speaker of standard English could distinguish [t̪æŋks] from [tæŋks], however.

One case that particularly interests me is whether th-fronting speakers can distinguish the /f–θ/ opposition in standard English. When I say the minimal pair free–three /fɹi–θɹi/, can th-fronting speakers hear the difference, or is [f–θ] an allophone in free variation for them?

Examples of standard English minimal pairs that might merge in these dialects:

• father/fava, mother/mutter
• thin/fin, thin/tin
• three/free, three/tree
• with/whiff, with/wit
• wraith/Ralph, wraith/rate

I don't think one can attempt to answer the question as is. By definition, if you merge, in production two sounds in your own dialect with respect to another (or rather rewrite one sound to an existing one), then two words that started in the standard dialect as different but are pronounced the same in the dialect are by definition indistinguishable (production or hearing) in that dialect. In some dialect, there is no distinction between 'three' and 'tree' there's just 'tree', spoken or heard, for the two different concepts. Only by definition, you cannot distinguish them if they merge.

Also, some rules are very context sensitive, those who say 'muvver' for 'mother' don't always say 'vin' for 'then' (oops, showing my pen/pin merger). So one may merge in certain contexts, but still produce and hear the unmerged context just fine.

Then, what truly is your question: are you talking about an individual speaking a dialect with a universal merge being able to distinguish them in another dialect where it is not merged? Then the answer, still by definition, is 'no', unless that person has enough exposure to the other dialect.