The ARM9 (don't think I have seen a compressed arm7 outside of a download play file) and overlays tend to use a slightly different form of compression to the usual type 10/type 11/type 40/BIOS LZ compressions seen in basically every other class of DS file.
Other than DS binary compression then it tends to be called BLZ
Cue's compression tools (the BLZ component thereof)
http://www.romhacking.net/utilities/826/ being what most would suggest for such things, though you might be able to get some of the all in one tools to do something.
I would also note if it is Crystaltile2 telling you it is compressed then it often lies. Usual way to check is compressing it and seeing what happens (if it compresses notably then it is probably not compressed, if it remains the same/grows then already compressed), seeing whether the code makes sense or seeing whether the code lines up with what you will dump from RAM (the ARM9 having to be decompressed, if it is compressed, and then put in RAM where it stays for the whole runtime.