Not really - the part that does the actual modem stuff is as closed as ever, that firmware doesn’t even try to replace Qualcomm blobs. What it does replace is the Quectel’s operating system - it’s like flashing another OS on a smartphone with integrated modem. It doesn’t influence your ability to detect things like silent SMS at all (maybe except of being able to offload diag data processing onto the modem itself).
When it comes to BM818, IIRC it’s using the same Qualcomm chipset as EG25, but unlike EG25 Broadmobi’s firmware does not appear to use Linux, so you would have to do the whole platform bringup by yourself.