This is one of the express purposes of the Sequencer Jack! Set the Sequencer Pedal Mode global parameter to "Trigger", send a trigger pulse from your drum machine, enable the arp and you're off to the races.
I haven't personally done this with the TR8, but the Sequencer Jack circuitry is designed to work with a wide range of output impedances from other gear. Just send a sound with a sharp transient attack, such as a rimshot, from one of the TR8's assignable outs to the Prophet Rev2's Sequencer Jack.
This configuration is inherently "beat synced". When configured as listed above, the arp/poly sequencer will progress one note/step at the moment a trigger is received.