FFG has said, "Moritat CAN use Powerswords, the key point is that it has a blade" (See Below). HOWEVER, the issue of whether or not they get tearing is up to the GM. Many lean towards toward only ones that deal R(ending) damage to get tearing, but there are also arguments for power weapons getting tearing. The key point is "Blades Okay" It is mainly the act of the slashing, which to Moritat is a holy ritual in of itself.
I just wanted to jump in and remind everyone that while it's perfectly fine to debate rules, don't let a friendly argument become personal attacks.
I also wanted to add a bit of clarification. The Moritat trains its operatives extensively in the use of bladed weapons—knives, swords, and the like. That is why they get tearing with them—they know how to precisely apply a blade to a living target in order to do the most damage. In addition, using other weapons (such as guns) is anathema to their training. Hence the Willpower Test.
Power weapons, however, occupy a bit of a grey area. A power sword certainly does not lack an 'edge.' It in many ways is a sword, and so the Moritat dogma does not proscribe it. A Moritat can use the weapon without making the Willpower Test—although traditionally the Cult encourages the 'traditional' bladed weapons, it recognizes that sometimes you simply need the most effective tool for the job.
However, power weapons do not get the Tearing quality. This is because although a power sword may fit with all the definitions of a sword in regards to Moritat dogma, it does not behave like a sword when carving through flesh. The power field on the sword (or knife, or axe) is what is doing all the work, violently disrupting flesh and bone and allowing a power weapon to cut through armour plating like a hot knife through butter (pardon the cliche). That very lack of 'subtlety' and precision, however, means a Moritat can't use a power weapon in the 'surgical' manner he or she uses standard edged weapons.
Or in other words, consider a master marksman. He goes to the shooting range with a semi-automatic pistol, and puts an entire clip into the bullseye of a target. Then, he reaches into his case and pulls out a 12-gauge shotgun loaded with buckshot, and shots the same target again. Did he hit the bullseye? Well, it's kind of hard to tell considering the entire target is now full of holes.
Hope this helps clear things up.