You can definitely get real acrylic that is transparent more or less to IR. I assume that what they are doing is more to do with the pigment than with the plastic.
IR leds for security cameras are in the very high end of ir before it becomes not ir. I haven’t looked up the laser frequency, but since I can cut transparent acrylic I would imagine I can cut IR transparent acrylic as well since it’s the same base stuff but with a different pigment. Here is a link to the very expensive e-plastics stuff. From reading around elsewhere many people find what they need by trial and error, some pigments pass the IR others don’t. The base is still all normal acrylic though so it should be able to be cut no matter what.