Is it grammatically correct to write
(property) is idiosyncratic to (object) in the same way that one could write
(property) is unique to (object)?
This feature is idiosyncratic to the Apple Macintosh.
It seems so. The Oxford English Dictionary has this 2002 citation from the ‘Atlanta Journal and Constitution’:
It may not, however, be common. The Corpus of Contemporary American English has only 16 instances, and the British National Corpus, 6.
It has the same basic meaning, though it carries a certain amount of value judgement. I take idiosyncratic as being somewhat negative, with unique being somewhat positive.