Q: Is it possible to get Sets / Sacred Uniques with the Chaos Reroll recipe?
A1: Yes, but Sets and Sacred Uniques require that the item have an ilvl of 121, so it'll only work if:
1) The item you're rerolling has an ilvl of 121. (Meaning, you got it in a level 121 area.)
1b) Additionally, bosses in level 118+ areas are also level 121, though this is less manifestly evident.
2) You haven't cubed (with any rerolling recipe) that item *at all* yet.
(Because the cube automatically caps the output item's ilvl at 99. Bye bye ilvl 121.)
3) You've stayed within ~1.5 screens of it, and haven't waited too long before picking it up.
(Because if you did, the game will unload the area (and the items in it), when when it 'restores' them, the ilvl will be capped.)
4) You haven't Saved & Exited yet.
(Because the game automatically caps all existing items' ilvl at 99 when you do. Bye bye ilvl 121.)