Crit IS nessesary.
Since you are mostly forced into blood presence every attack on your target must count because of rune downtime, thus crit being one of the main stats for Unholy. This isnt cata anymore, crit is actually vital to DKs, 2h Frost DKs take crit as their main stat, Unholy PvE take Crit as their main stat as does Unholy PvP.
This is Volkovitch.. EU's highest rated DK back on Grevious season... 10k Crit rating > 8k Mastery > 4k Haste rating...
http://web.archive.org/web/201409270...kovitch/simple
Cervantes of Outland EU (current rank 3, cant remember his S14/15 rank).... again taking Crit rating.... 11k Crit > 6k Mastery > 2k Haste
http://web.archive.org/web/201402141...%A1ntes/simple
But Hey what do I know? I only spent the entirety of Season 14 (grevious) and 15 (prideful) on retail as an UHDK.