Does Linux ever hard freeze?
Been using ubuntu since 2006,
Got lucky and have never experienced it.
Yes it does... Of course it historically has always been more stable than, say, Windows, but hard freezes can and do happen mostly for these two reasons: kernel (including modules) bugs, and hardware issues, as pointed before. More rarely, a bug in the "init" process can also do this. These can trigger what's called in the Unix world a "kernel panic", the equivalent of Windows' BSOD. In some cases, even in a kernel trap, you can do some debugging (like dumping memory) and take a few actions, like syncing the filesystem and rebooting, but not always.
That's one of the reasons why enterprise and "stable" distros (RHEL / CentOS, SLES, Debian stable, Ubuntu LTS) are more conservative with new kernel and software versions. They tend to use the long-term kernel tree, which doesn't introduce too many features, focusing more on fixing bugs.
Now, personally, with nvOC (which uses Ubuntu LTS) I've never had a kernel panic.
But you never know, if you need full remote control this SRR seems a cool addition, or an intelligent power switch, KVM etc.