Yes, as long as you pay attention to what packages are being added and removed when you perform an update. Once in a great while, there have been instances of buggy packages mass-removing other packages due to a bug.
That said, Debian-based distros like Ubuntu usually base their stable releases on unstable. Unstable doesn’t refer to software stability. Rather, it refers to the idea that the system-level packages could change throughout the development cycle.
Security updates come to unstable through normal package updates, which testing doesn’t get until everything makes it through a probationary period with no “serious” bugs filed and no dependency issues. And if any package that the package needing the security patch depends on also has a serious bug filed, the process could take even longer.