For all intents and purposes, yes. Besides making software easy to install, package managers figure out all the dependencies that a given package requires and install those as well. Can you install yum/dnf on Debian? I'm sure there's a way to do it. But good luck handling all the dependencies for a given package. Plus, there will be file conflicts when dnf installs a base dependency that apt already installed.
In other words, nothing good comes from trying to install two different package managers on one system.
In other words, nothing good comes from trying to install two different package managers on one system.