The Omicrons can run effective simulations, Holodeck-style, which we saw in the Stigma Dreamscape that you needed to do to unlock the Omicrons (but understandably probably did so quite a while ago). That's what they're doing to bring in life forms from the Dead Ends, and apparently the simulations are real enough to be effectively indistinguishable from every other life form in Ultima Thule, as evidenced by the fact they can manipulate dynamis.