sure, within reason. I wouldn't try to build a product in a language where the available labor pool is tiny given the problem domain. For example, don't build an enterprise SaaS platform in pure x86 assembly; don't write device drivers in Delphi.
Eeeh. Having a small but not tiny labor pool can be beneficial in that the programmers you get are probably better than average, since average people don't tend to learn off-path languages.
Rare skills tend towards the expensive, either in money or time-to-recruit, or both. It can sometimes be worth it for specialist tasks, but I'd be cautious.
