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.