Personally, I don't see where it maters, you're putting 60 Hz. AC power in, running the idler motor at or near its synchronous speed & getting 60 HZ., 3-phase out, regardless of what the motor's doing. If you have a choice a 4-pole might be better only because it runs slower so bearings would last longer, it'd be quieter & possibly vibrate less.
the frequency may be at 50HZ in SA.
but either motor (2p or 4p) would suffice regardless of frequency.
i would look for a 4 pole motor myself.
if your oven requires 3 phase to operate, then yes you can hook it up to the rpc
on the other hand, if your oven operates on single phase, hooking it up to a RPC would be a waste of time and energy
If the oven is not new, you may have problems with the elements, wiring, connections, and stand offs crumbling as you try to work on them. In that case I would stick with three phase if that is a good possibility.
A quick look at the oven wiring could be simple enough.
Likely has 3 heating elements one each across each phase.
Depending on the voltages one could connect single phase to some connections and have it still operate but at lower output.
The oven should be built such that the area where the wiring from the heaters to the distribution blocks is servicable so it should not be difficult but the voltage rating of the heaters could make things interesting.
The oven elements are resistive loads, the elements are usually wired to a terminal block and it is the configuration at the terminal block that usually determines if it can be rewired to run off of single phase. The elements are in banks so probably star for 240V 3 phase and parallel for single phase. If the manuals states that this is OK to rewire for single phase, I would go that route, a RPC is not needed. Other considerations are if there is a controller and what voltage it needs, you will also need to change the input wiring gauge to the terminal block and breaker so it is compliant with the increased single phase amperage.