Can Dalinar permanently bring someone back from the Spiritual Realm?
No. In fact, whether or not the voices he is hearing are legitimately voices from Beyond the Spiritual Realm, or if they're a manifestation much like the visions that the Stormfather creates, where Dalinar's desire for certain things is basically creating... So when Dalinar goes into the visions, what's going on there is: these are not people with autonomy that he is interacting with. These are Investiture manifesting a basic AI that is able to adapt, cause Investiture kind of can do this.
Dalinar would argue, "Yes, that's the case except for when I actually met Nohadon. That character felt different, that felt like the real Nohadon stretching through the Spiritual Realm and actually interacting." Jasnah would say, "No, that's because, Dalinar, you have such, in your mind, a hope and desire to see Nohadon, he's this mythological figure in your head, that basically the Stormfather's knowledge of who he actually was was creating this much more animated puppet that was more like actually how Nohadon was, but was based on knowledge of the spren and the Investiture that you're interacting with." And Dalinar would say, "I heard Evi's voice." Jasnah would say, "You heard the Investiture coming to life and speaking with her voice the things you needed to hear. And it wasn't that the Stormfather was like, 'He needs to hear this, I'm going to create this fake.' But it's instead your relationship with this magical force that does take on life of its own, manifesting this thing." Which one it is, I do not answer. Both are, I consider, equally valid interpretations of the text, and equally valid interpretations of the magic system.
Once someone is passed into the Beyond, there is no force that can bring them back, according to people's understanding of the magic system. There is even the argument that Cognitive Shadows are not the person. That the Cognitive Shadow is indeed a spren with the memories and an imprint of the person's personality that becomes self aware and continued on living that person. It's kind of the same question that arises in Star Trek. When you are ripped apart and rebuilt piece by piece with the transporter, some people in Star Trek do not believe you are becoming the same person again. You are then a different individual who has been cloned from the person and had the memories attached. Functionally, in the narrative, for the reader, it's the same. Is it the same soul or not? That question is answered differently by different people in the Cosmere. There are equally valid interpretations from the reader. You get to decide, basically. You get to decide, just like if there's a story where a person's brain is uploaded to a computer, you get to decide: is that the same person? Because we can't do that, we don't know. Is that the exact same individual, or is that a computer simulation of that person, where the person has died? That's what a Cognitive Shadow essentially is, but using Cosmere physics instead of theoretical science fiction physics.