I'm just starting to really learn Blender, and I'm having minor issue I need help with.
I'm editing part of a mesh someone else created for an outfit. For no reason I can find myself, the sleeve was split off from the chest region as a separate mesh. I would like to avoid any chance of a seem opening up with certain animations or the two clipping oddly, so I wanted to physically link the two meshes together, but I don't know how. I could probably paint extra faces between the two, but that would screw up the UV.
Anyone know of a way to do this?
I tried using "Join Objects", but not only did that not physically link the two (merely connected them as a single selection), I also don't think it stayed after export (I also may have botched that export, so I'm not sure).

Another minor issue I just remembered; when I select the whole outfit with A and deselect the skeleton, then go to Parent the outfit by pressing Ctrl+P and selecting Link to Armature > Don't Create Groups, I have to click "Don't Create Groups" like 10 times before it finally goes through. Anyone know what's going wrong there?

Separate parts don't have to be connected to be considered one "mesh". If the single-selection object is of both parts, then both parts are the same mesh. Is that on-track with what you needed?

Also, if you are trying to parent the outfit to the skeleton, both it and the skeleton must be selected.

That isn't the issue. I can't perfectly align the two meshes with each other just by moving them around, and I wanted to avoid a possible seem from showing when the character moves certain ways, or having visible clipping because I put them too close together.
Since they appear to have originally been one mesh, I was hoping I could re-link the vertices so they would be perfectly aligned.

I tried keeping both the outfit/mesh and the skeleton selected (with the skeleton primarily highlighted as I assume it should be from tutorials), but the issue is still there in which I have to select "Don't Create Groups" many times over before it seems to go through.
I click on it, the window goes away as it should and immediately reappears (often moving to center on the current position of the cursor).

Select the mesh, then the skeleton, and you should be able to select "Make Parent to Armature".

I can't seem to visualize the other problem. I'm not a great audio learner. xD

Actually arms and torso are often seperated for a reason. You need to give the arm parts different attributes in NifSkope, if you want them to be visible in 1st-person view, while you clearly don't want that to be the case for many torso parts for several reasons.

Though if you really want to merge them, do like you did, first "join" the seperate objects. Then select all vertices in Edit Mode and select "Vertices -> Remove Doubles" from the menu. This should make the identical vertices at the connection line become one each pair and really combine the mesh. Now you only need to make sure both sets of vertices use the same material record as well, as this is what the NIF scripts use to re-seperate them again afterwards. It's quite handy to be able to get your individual meshes seamless by joining and merging the connecting vertices, but when you export it they will be nicely seperated as before again, unless you messed up the material assignments.

As for the multiple-selecting thing for parenting to armature, well I could imagine this is due to you doing this step for such "joined" objects without these vertices actually being made into 1 set ever. I could imagine it asking you for every "set of vertices" in the joined object, especially when it's to decide about the "vertex groups".

Thanks, that was a huge help.

Bear in mind that when you export from Blender, sections that are different materials will become separate NiShapes/Strips anyway. As long as the vertices at the seams are indentically weighted to the skelton/armature they won't separate during animation, so it's not really an issue. The arms are usually only "disconnected" in order to make UV mapping easier, and the seam vertices will act as if welded in-game.

It turns out the multiple messages isn't just a separate one appearing for each piece of the outfit. I counted it, and it appears 29 times. A little extreme.
Also, I tried exporting the outfit then importing it again, and the vest came back as some mixed up checker-pattern of black and gray (it was all black initially).