No, Amazon echo MRM groups typically take their input from alexa cloud supported services and don’t support local external input.
Amazon’s Echo Link (in the USA) does support what they call line-in distribution to achieve what you want , but that’s not a feature of WiiM devices. Plus you’d need something to accept your DLNA Server output then connect that to the Echo Link aux input.
Edit: while some older echo models do have a line in, that’s just for individual devices, again they can’t then send that to other devices.