Art nicely surreal? Yes! (9)
I believe the answer is:
certainly
'yes' is the definition.
(I've seen this in another clue)
'art nicely surreal?' is the wordplay.
'surreal?' indicates anagramming the letters (I've seen 'surreal' mean this).
'art'+'nicely'='artnicely'
'artnicely' is an anagram of 'CERTAINLY'.
(Other definitions for certainly that I've seen before include "Without doubt" , "By all means" , "Definitely, surely" , "Definitely, positively" , "Thirty seven [37D=WITHOUT FAIL]" .)