Are there dialects of YAML or just differences in parsing it?
There is only one YAML spec. That would lead me to say "There are no YAML dialects". There are certainly differences in implementation, perhaps due to what the article claims as the spec's ambiguity:


  YAML specification is so ambiguous,


It's a matter of opinion, I believe, but there is no doubting that various language-specific parsers of the same data result in different output. So, to answer the question(s):


no there are no YAML dialects (since there is one spec)
yes the spec provides much leeway for implementation and thus there are differences in how it is parsed.