I don't mean to be combative, but I think Gentoo and PHP both have their place. I can guess why you would think those things would make an engineer unhireable, but that didn't always mean trouble. I would assume the real problem would be when an engineer limits his/herself to those things and can't work outside them. An engineer that only knows how to work with PHP or refuses to use anything other than Gentoo can be a large problem.
I started with Gentoo and PHP. I know them both better than most. I have several commercial products that went into production written in PHP and deployed on Gentoo systems.
It was dumb then, but I was 20. It’s still dumb now, 15 years later. Those people had no business hiring me then but they were even dumber about technology than I was at 20.