The RM32AI sends all signals (inputs and outputs) in the digital domain, which means that all analog inputs and inserts do not receive any signals. As far as I remember the four DB25 connectors also belong to the analog domain, so you probably can't use them. They are actually meant for the purpose you describe, when the FOH console is dealing with analog input signals. I am not sure how the situation is with the local outputs (auxes, mono, main), but I am sure you can test that.
The DB25 connectors of the RM32AI handle aux outputs only, but that doesn't help you either. AVB first generation had the limit of two hardware units corresponding, so only conventional microphone splits can help you. Or you use aux mixes 15+16 (!!!) of the RM32AI for streaming. For this the RM32AI has to work as monitor mixer and all mixing of the aux mixes has to be done via UC Surface. It might well be that you can use the 14 aux mixes of your SL3442AI separate, which might open even more options.
In Monitor Mode you can even use the main mixing level of the RM32AI. This sum is available at the headphone output of the RM32AI only. Mix via UC Surface at FOH and send the signal to the streaming unit - that's probably the best solution. Effects are available for this mix as well as for the 16 aux mixes.