I don't know about Tanner, but Hartley is definitely not fit. Based on what Robinson said yesterday, it makes even more sense now that Aldred was brought in.
If Tanner isn't fully fit, it makes sense to save him for Wed, when he can play a bit more football.
If Tanner is fully fit, I'd definitely have started him - but it can't be a surprise to anyone now that Robinson likes to pick his 11 biggest men against teams like Accies and Hearts.