People seem to think that Uber will be running into Truth. Which... I guess that can happen, if he makes a mistake, but as far as I understand FMA alchemy, manipulating souls is completely fine. You can put them in stones and use them as batteries, you can even put them back in their bodies if those bodies are still intact. In fact that will happen naturally. Souls want to return to their bodies if that's an option. You can bind them to objects, have them pilot suits of armor around, and put multiple souls in the same body. There's nothing stopping an alchemist from messing around with souls to their heart's content.
Uber's goal is completely possible.
As long as he knows what he's doing, that is.
It's a ridiculously difficult procedure, more complex than anything anyone but Father and maybe Hoenheim did in the canon show. Fixing a body as messed-up as March's is basically on the level of Homonculus creation, and transfering her soul from her shard and into her newly built body may be as difficult as the Ling-Greed transformation was, and Uber, unlike Father, isn't a knowledge spirit born from the living universe, nor does he have centuries of experience with alchemy and a philosopher's stone 500.000 souls strong.
But he does have a parahuman shard, which we all know are completely bullshit.
And the fact that March's Shard is probably all for resurrecting March means he might actually be able to manage it.
Truth doesn't block human transmutation. Truth steps in when you're going against the laws of nature. That's what Truth is. Truth are the laws of nature, and one of those laws seems to include the cycle of souls. You can't call souls back from the afterlife. At least not with alchemy, because there is no equivalent exchange. There can't be. Souls are invaluable, and they're uniquely invaluable, so you can't even sacrifice one soul to get another.
That's not a problem if the relevant soul is within your grasp though. Then you can manipulate it just fine as long as you know the rules.
Victor can't succeed because his goal is to resurrect a person who's soul he doesn't have access to.
Uber can succeed because March's soul is hosted in her Shard, and her Shard is probably helping.