There are lots of characters who say little to nothing. Some people are naturally more reserved than others.
Jacques seems to spend a lot of time daydreaming, and generally is respectful of people's opinion. So yes, he says a lot of weird things in a group of mercs that regularly insult each other, and tend to only discuss things in the moment.
Nobody ever says he is emotionless, the only claim made of his emotion's is that he isn't as horny as Ace, which isn't hard.
I presume he was a lone hunter before joining Geddoe, so he probably just enjoys being alone in his free time, and particularly alone with nature, which is often where he goes when given the free time.
although someone with Autism might have these traits, I don't think they represent Autism, or even a disability, just a lifestyle. Certainly Jacques isn't suffering it if he has it.