After completing the DLC I've become aware that the new rarity level items can only be purchased (with a special currency). I didn't notice any oranges (period) while playing, particularly new oranges, though I noticed a few unique (probably common) drops from bosses.
Are there any rare (legendary/orange) drops in the Captain Scarlett DLC or are Seraph weapons and the new blue Uniques the only new equipment?
There is no new legendary items unique to the DLC, only some blue and purple rarity items.
And regarding the Seraph crystals, they no longer drop on normal/TVHM, only on UVHM.
Both raid bosses hyperius and master gee have chance to drop variety of legendaries from the main campaign and some seraph items.
Generally the Sandhawk and Rapier are the only worthwhile items on the DLC and they are both easily obtainable by just playing through the dlc.
Leviathan's lair has a pretty good chance to drop great relics and mods.
There is a lot of new loot in this DLC. There are new unique items, the seraph (pink) items, a lot of white, green, blue, and purple items, and new e-tech items. There are no new orange items that I've seen. However, the raid bosses do drop some of the old orange weapons. The armory at the end of the game also has a pretty high drop rate for orange items.