What do you mean by a looper pedal? If you mean a digital looper/sampler, you need to get your head around the kind of things that you can connect to amp outputs (ie speakers, attenuators etc, not pedals), and the kind of things that will drive speakers (ie amps rather than pedals).
If you mean just a splitter, 1 in 2 out, not switched, all wired in parallel, then that should work, though it needs wiring / cables which are suitable to carry line type power levels. Don't use a guitar cable to connect speakers.
If your amp has a tube power section, you must never risk the speaker circuit becoming open circuit.
Whereas if you amp has a solid state output section, you must avoid a short circuit on the speaker circuit.
Sorry, should have been more specific. At's an A/B | A+B pedal. I want to run 2 8 ohm speakers in A+B mode which would run the speakers in parallel. Something I don't have the option for currently due to the single jack on the amp and on each of the speaker cabs. Of course I'll be using speaker cables. The concern is the 20-22ga wires used inside the pedal.