If I am running a Middle Tor Node, is it possible to get malware from malware going through the node?
That's a pretty broad question.
It's possible that there could be a bug in Tor or one of the libraries which it uses that would allow someone to attack Tor relays and run malware on them.
Under normal relay circumstances the harm done would be limited in impact due to restrictions on the Tor process. Running under a MAC like AppArmor as a low privileged user. In the absence of another exploit, against the kernel or another privileged service on the host, it would struggle to do more than simply corrupt the Tor process until it was restarted.
Such attacks are possible, which is why the Tor process should be restricted to the least privilege possible and confined to reduce the impact of such an attack.
As far as I am aware hasn't been publicly documented as happening "in the wild".