In order to minimize potentially compromised software from reading what I'm writing in Veracrypt I want to use the software inside an encrypted guest OS with no Internet, specifically Ubuntu 16.04. Does this minimize the chances any piece of software in the host OS will compromise TrueCrypt?
Not in any way. Host software (eg. kernel rootkit) still has access to everything ie. your encryption keys inside VM's RAM.
Usually you use virtualization to protect the host against hostile code, so that the code running inside the VM can't harm the host (and there are still loopholes). There is no way to protect a VM against the host.