You cannot have multiple sound files, ever. Errors will occur. You need to load the Hoth sound file in your mission script then edit the weapon ODFs from the AT-ST to use reference the AT-AT weapon sounds.
If you're putting the msh/odf assets in your SIDE then the class entries also need to go in the SIDE req, as well as creating a subreq for the class name, then call up those assets alongside the normal SIDE assets in your mission script.
Then apply the class drops to the character ODFs.
I can't say this will work but it seems like it should, I have used similar methods for getting content loaded into BF2.
This is BF1 afterall, one of the jankiest games of all time (Still love it) so it may not work.
The patched ISOs that I prepared don't require manual DNS and the DNAS was removed. All you have to do is load those ISOs I made and make a new network configuration file as you would normally as if Gamespy still existed.
I've had this issue several times when making maps in the PSP version of BF2. Every time I solved it by playing around with the sky file values inside NearSceneRange and FarSceneRange. Several times I just copied values from vanilla maps and they worked perfectly.
The method I've used several times is to take a copy of Mos Eisley, toggle terrain off, erase the sky dome block of code from the SKY file, clear out all the regions, paths, props, etc then re-add what I need in any of the layers, then load that after my real world was loaded.