Yes, you use 'rpm-ostree' to install and manage regular dnf packages, or local .RPM files.
The limitations are:
1) Each invocation of the package manager (install/upgrade/uninstall, the usual stuff) results in a new OS 'commit' and requires a reboot to switch to it.
This is the entire point of the distro (random .rpm broke your system? just rollback), and is why Silverblue users generally only use DNF packages for low-level tools and run regular applications as flatpaks, appimages, or podmans.
2) Occasionally you'll run into a package that wants to write to a folder that Silverblue made read-only and version-controlled, and breaks. In that case your only options are to run the package inside a toolbox (a special Podman container that comes with Silverblue for these scenarios), or patching the package.