Just my opinion here, but based on the scenario you have described, I would take the Guardian and Conservator appointments out of the equation for the purposes of the trust. The trust is a separate arrangement which stands outside of the realms of Guardian and Conservator.
The Guardian has been appointed to manage the physical affairs of the disabled person. That does not prohibit them from also creating and funding a trust for the benefit of the disabled person, or from naming themselves as Trustee of the trust.
This is not a case of the Guardian having monetary powers for the disabled person because the source of funding for the trust is coming out of Guardians pocket, not the disabled persons.
Just be careful about what you are using as the Trust TIN. Depending on how it's drafted, it should use the SSN of the disabled beneficiary, or it's own EIN. If it is using the SSN of the beneficiary, the Conservator may come into play to sign a W-9.