Damn, so there was capital letters I overlooked. Does this mean that your specific Linux distro d3 ignores material files with capital letters??
Yesh, since usually D3 cannot tell that "FooBar.Baz" should be the file "fooBar.Baz", "foobar.baz" or any other combination thereof. An exception is if you specify as asset "Foobar" and there is an all lowercase file "foobar", then D3 will load this as a sort of last-resort. But if you specify "f.bar" and the file is named "F.bar" D3 has no chance.
(I wonder tho why it didn't load "Custom.mtr" as these files are not referenced, so it should just load all mtr files it finds. Strange)
As for the dmap, this is an unsolved mystery, some maps need a dmap on linux, some not, and so far we don't know why. Bikerdudes missions didn't need a dmap for me on Linux. Maybe it has to do with the map file being "Foo.map" vs. "foo.map", too?