As for the "Plexiglass" does anyone know if its even possible that a material of this kind could contain lethal levels of radiation?
Certainly. It's very good for that purpose in the real world, in something like three ways.
Anything that stops small particles is good for containing radiation fallout: generally, the radiation-protection suits worn in nuclear powerplants or the like are made out of dense, strong paper, or material like that, because that's more than sufficient for preventing the radioactive particles from reaching your skin. Plexiglass would actually be overkill in stopping radiation sources from "flooding the whole compartment" in that sense.
As for the actual radiation coming from those sources, much of it can be stopped by paper. The heavy nuclei resulting from radioactive decay can't travel through more than a millimeter of polymer-like material, so again the paper suits are good enough, and thick plexiglass is overkill.
Some radiation is more penetrative than the heavy nuclei, though. The most penetrating sort is electromagnetic - gamma rays, x-rays and some longer wavelengths. Here it so happens that plexiglass walls would probably be superior to transparent aluminum: light metals, let alone heavy metals like lead, would just get all excited when bombarded with EM radiation, and this might cascade into additional radiation created by the lead shield, but polymers (possibly thinly spiced with lead, tungsten or the like) absorb many EM frequencies "gently", without creating cascades of nastiness. They are also very good at stopping the intermediate threat, high-energy electrons (and positrons), without adverse effects other than possible accumulation of electric charge.
I'd say a room where emergencies may cause the leakage of radioactive gas or steam clouds would indeed be well protected by such walls, then. And the revolving door would also be a fairly good construction for an airlock.