So we are having a girl this spring, our third daughter. Our two girls have very Scandinavian names because of family heritage and we wanted something that went along with that but was easy to use. My husband and I have stewed over names for months and really love the name [name_u]Finn[/name_u]. It has that Scandinavian feel, but is “user friendly”, a hard combo to come by. The problem is my brother had a dog with this name that has passed away. Does this make it “used” and off limits? Thoughts…
If you liked the name, then yes.
There isn’t a big scroll on the mount that says what are dog vs. human names.
Except Spot and Fido maybe. 
I think it depends on a few things - how long ago did the dog pass away; how would your brother feel about it; does it bring the dog to mind when you say it or think about it, etc. I guess, do you (and/or your family members) still think of it as the dog’s name?
These are my thoughts.
Personally I would not want to choose a name that could bring up sadness for my brother (or anyone else). In this case I would ask him his thoughts.
If it were my own dog? Sure, I’d use the name anyway. However, since it isn’t, you should just ask your brother what he thinks about it (as previous posters have suggested.) If he doesn’t mind, cool. Once the child is here and named, it won’t make anyone think about the dog.
I have a cat named [name_f]Stella[/name_f]. I adore the name, but I don’t think I could ever use it for a daughter after having used it on my cat. However, I would be ecstatic if a sibling wanted to use it so that I could have a niece named [name_f]Stella[/name_f]. I’d run it by your brother, but ultimately the decision is yours, and I think you should use it if you love it and it feels right.
I agree with pp, you should ask your brother. Otherwise I wouldn’t think twice (But my second dd’s name is also the name of a cat my mom and I had for nearly 20 years and I would consider a version of Mauri/[name_m]Maurie[/name_m] for a girl, which is the name of a cat I had for nearly 13 years).