It is works with ASTC_RGBA_6x6, but don't work with ASTC_RGB_6x6.
UABE defines a ASTC_RGB_6x6 texture as a ARGB32 texture, gives an error "Unable to convert texture data!" when been used export plugin on the texture.
I tried change texture format from ARGB32 to ASTC_RGBA_6x6 in the edit option; and then the texture has been converted in tga without any errors.
But it is not the solution for batch convertation.