The problem isn't that mono (or programs written using mono) have portability issues themselves. Requiring mono itself is the portability issue. Many people don't like running mono or .Net runtime or even the Java runtime and some businesses/clients don't want to support it. That is quite a portability issue.
How do (or would) you deal with architectures that Mono doesn't currently support?
I probably wouldn't purchase those servers.
Sometimes you have to deal with what you have, not what you want.
Ah, sounds like an excellent approach to "portability". Good luck with that, but be sure to let me know when you return to the real world.