:As to your question:  yes, El Diario is a perfectly good source.  Your summary of the article, though, isn't accurate.  It's not clear from the translation if "" is what the author thinks GG needs to do, or what the author thinks that GG thinks they need to do, but in context it definitely cannot mean what GG has been doing.  As to the linking, what I'm reading is:
 Emphasis added.
  Emphasis added, translations by google.
It's not clear to me how you get from that to your claim of "ethics did indeed form the motive for criticism of Quinn".  The author of the article has gone well out of his way to state the exact opposite is the case.  (Just in case you're not familiar with the idiom, excuse in this context is the reason given to mask the real reason, which the author details in the preceding paragraph.)  I'm more disturbed by the fact that you think finding a single source is sufficient for getting a WP:FRINGE viewpoint into the article.  
You may be able to dig up a journalist who does think that ethical considerations motivated the behavior.  That shows you found a journalist who had an off day; it happens sometimes.  Given the amount of coverage we have to select from, I'd be expecting to see a half-dozen pieces expressing that viewpoint for it to be considered a legitimate minority view.  Despite lots of motivated, net-savvy folks looking for those pieces, they're still nowhere to be found.  This gives me high confidence that, for the population of adults who write for a living, the idea that ethics motivated GG is simply not worth writing about (probably because it's not remotely plausible, but I don't have to reach that conclusion here).  
So yes, we're good to use the article, but as it doesn't add anything to what we currently already have, I don't see a compelling need to do so.