Thetan is allowed anywhere except the Neoplasmic Lattice - Orthorhombics have very good visas - but if he went to the Xenodrome without a clearly filed agenda, or to the Hegemony Orthodrome not in the company of a resident, he'd be under heightened scrutiny.

Elevator clearance to the planet requires a work visa - he'd have to come up with a reason why he needed to go in person and get a supervisor to sign off on it. If he did that, he could go anywhere on the surface he wanted, but he could expect his reason to be checked against the time he spent down there and the locations he visited.