1. Are they relying on any OS X software? For example, at my last job the front-end developers relied on Codekit, an app for compiling CSS, etc. Now, it could totally have been replaced with Gulp or similar - but do you want the first thing you do when you join the firm to be proposing they alter their workflow around you?
2. Whilst you work best on Linux currently, perhaps you could learn to use a Mac too? Then you have experience with both platforms. You could always use Linux in a VM as a backup too.
3. If you have issues as the only person running Linux, you'll have a harder time fixing them and people will have less time for you. I've seen this a number of times. People choosing something different to the rest of the team because they prefer it and it improves their productivity, only for it to cause trouble (rarely their fault) and them get looked down upon because of it.
Overall, it probably won't matter - but it might be worth thinking about it. If there were some other people running Linux too, I'd say go for it. If you're going to be the only one, you might end up making too many waves - it's up to you if you're comfortable with that.