are you going to install nix in a random docker container?
For example, in $CURRENT_JOB we have a bastion host that gives access to the databases (not going to discuss if this is a good idea or not, this is how my company does). 90% of time I can do whatever I need just with what the bastion host offers (that doesn't have Nix), if I need to do further analysis I can copy some files between the bastion host and my computer to do further analysis.
I can just drop it into the environment and pull in tools that I need using nix.