I know that there was at least one of them... However, i must mention that that dragon IS NOT EBONMAW.
Who is Ebonmaw?
https://vignette.wikia.nocookie.net/leagueoflegends/images/9/96/Ebonmawscreenshot.png/revision/latest?cb=20151004011858
A Zaunite dragon from the old Twisted Treeline, before the rework... Known as "The Terror of Zaun". Since Ebonmaw is from Zaun he has never been in The Shadow Isles.
But why im talking about Ebonmaw?
Well, since he was the Boss Monster from the old Twisted Treeline, people has made connections between him and a dragon skull that appears in the lair of Vilemaw, the Boss Monster from the new Twisted Treeline.
http://3.bp.blogspot.com/-w8IcBt8V3bI/UH9cXb32b8I/AAAAAAAAJAk/pUUDLdcxQ8k/s1600/vilemaw.png
And that is the point of this post... as you can see in the picture, there was at least one dragon that lived in the Blessed Isles, but he was killed by Vilemaw (that is why he has a skull of a dragon in his lair), and that dragon as i mentioned, is not Ebonmaw since he does not live in the Blessed Isled.
And YES RIOT SAID THAT THE SKULL IS NOT THE SKULL OF EBONMAW