I'd agree it's better to run the enable signal to the drives rather than switch the DC. I don't see any role for an SSR here either, other than coolant etc.

As you say, it's simpler to run an AC side contactor on an e-stop circuit if you can be bothered, rather than switch the lower voltage DC side. Personally, I'd rather not throw everything out each time I hit the e-stop but that's a matter of preference.