UMD has th following sub-skills:
Activate Blindly
Decipher a Written Spell
Emulate an Ability Score
Emulate an Alignment
Emulate a Class Feature
Emulate a Race
Use a Scroll
Use a Wand, Staff, or Other Spell Trigger ItemA Shard of Psychic Power is not an activated item. It does not need deciphering, it is not ability or alignment dependent. You already have the class feature needed.
Therefore, UMD has no useful interaction with the shard.
/cevah
It seems to me that if you have the needed class feature that you can then cast the spell. If an occultist cannot cast the spell (by being in a "forbidden" school), then they obviously do not possess the requisite class feature.
To the OP, my opinion would be that using a Shard of Ablative Barrier would require a UMD roll of 24: 20 to emulate the Conjuration Implement, +4 to reach a caster level of 4 (the caster level necessary to cast 2nd level spells).