I don't think he needs to feel bad about increasing his salary. Make it 200k/yr and make his life easier, which can only be good for the project long term.
(Some) HN commentators seems weirdly out of touch when it comes to salary outside of IT-heavy cities in the US. The other day someone claimed $125k/year for an employee wasn't "big money" (https://news.ycombinator.com/item?id=40927175), so I'd take any comments saying some salary is high/low with a box filled with sand.
It's comfortable outside of Paris and other expensive cities. But he could easily double that given his background. Before quitting his job he already worked with Play and the Typesafe (now Lightbend) stack before the peak of its hype, when companies were paying top dollar for consultants.