One sane Dubliner, in short, turns out to be impartial (8)
I believe the answer is:
unbiased
'impartial' is the definition.
(similar in meaning)
'one sane dubliner in' is the wordplay.
'one' becomes 'un' (northern English dialect form of 'one').
'sane dubliner in' becomes 'biased' (I can't explain this - if you can you should give a lot more credence to this answer).
'un'+'biased'='UNBIASED'
'short turns out to be' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for unbiased that I've seen before include "Not partial or prejudiced" , "Not favouring one side or the other" , "Impartial" , "without side" , "fair" .)