I've just heard the clip. I wouldn't say that Breton sounds like Welsh, but he doesn't sound French either. He has a nasal 'o' which French has, but this would more than understandable because the two languages live side by side, and French has been dominant. The second man definitely has a French accent.
Benjamin, people tend to get quite sensitive over this issue with native accents. I can usually tell if someone has an English-only speaking parent because it will come through in their accent when speaking Welsh, although it can be very subtle (or not, it depends).
Tegs, I used to think that if someone had a strong south Welsh accent, then that would mean they would be able to speak perfectly with a natural accent when they learnt the Welsh language.......but not so! I've heard people with a strong south Valleys accents speak with a terrible accent when they speak Welsh, despite knowing how the words are meant to sound like. This is because English requires you to use different parts of the mouth, and Welsh requires you to use other parts. This influences your mouth over time, and I'm guessing it it's the same with Irish Gaelic. For example, many non-Welsh speaking people from south Wales, despite having a strong accent, do not roll their 'r' anymore as they have adopted the English pronunciation,(the 'r' in Welsh language is always rolled).
A lot of northerners in Wales think that southerners sound like English people speaking Welsh, and this is why we often find them so hard to understand. It's true to certain extent. When a lot of southerners speak Welsh their vowels are quite undefined and sloppy, for lack of a better word. Welsh vowels are meant to be open and sharp (you'll hear these sorts of vowels in Spanish and Italian as well).
The reason for this because a lot of southerners learn Welsh as a second language, often at school. Even if they speak it fluently, they still retain this Welsh learner accent (and they won't necessarily have a native speaker teaching them Welsh). You can hear a lot of this accent in the south east, where there's been a strong push to revive the language. It's now common to have grandparents who spoke a bit of Welsh, parents who don't speak any, but people under the age of 28 who speak it to an intermediate - fluent level.
However, I'd like to point out that a pure southern accent does exist, but sadly it is much rarer. Of the Welsh speakers I've met in south Wales, only 1 out of 10 or even 1 out of 15 will speak with this pure south Welsh accent.
It's really interesting that Breton has two 'u' sounds. It's interesting because Welsh has 'u' but it has a flatter, less rounded sound than the French 'u', and it comes from the very front of the mouth. It's like Breton has kept the celtic 'u' and also adopted the French one.