Hi Craig,
I do believe Rekordbox uses the standard ID3v2.4, ape tagging specifications.
You must trim the YEAR to four digits, and RELEASETIME is the Release Date, which must be using the format YYYY-MM-DD, so if you have tags using the iTunes Release Date format of YYYY-DD-MMT00:00:00Z will not be read by Rekordbox.
FYI other tags supported by Rekordbox are:
ORIGARTIST (Original Artist), ORIGALBUM (Original Album), ORIGYEAR (Original Year), SUBTITLE (Mix Name/Version), MIXARTIST (Remixed, altered or interpreted by), BPM (Tempo), INITIALKEY (Key).