Is it still true that Marketo only supports emojis of Unicode 5.2 and earlier?

I tried to use a Unicode 6.0 emoji (Q-encoded) in the subject line of one of my emails
and it rendered fine in all but a handful of email clients.
I then swapped in an older Unicode 5 emoji and it displayed perfect across all email clients.

Just wondering if it's still the rule in Marketo to only use older emojis : Unicode 5.2 and earlier