Those are TRS-80 disk image files.
In theory yes, it should be possible to convert.
You might try the HxC emulator disk tool. The page indicates it supports DMK format, and it can write a very wide variety of formats including ImageDisk, as well as Kryoflux and SCP streams. From my experiences so far though it is not always 100% reliable with conversions.
I don't know if there is a tool for more direct conversion.