If I recall correctly, Alpha was important in the history of the Linux kernel. Originally the Linux kernel only worked on Intel chips, but the effort to modify it so would also work on Alpha set the stage for it to run on many architectures.
The Alpha folks talk about being the first port away from x86, but Linux/m68k (1993) predates the Alpha port (1995). I guess the difference is that m68k was happening independently and lived out-of-tree for a long time, while Alpha was happening with the direct involvement of Linus and lived in-tree from the start.
I think the Alpha port may have been more significant because it required making Linux work on SMP systems with a very weak memory ordering model, in contrast to x86's strong ordering. I'm not aware of any SMP 68k systems, but that was definitely an important part of the Alpha ecosystem.
