Just to be clear, the Rominator is an IIsi ROM image with some QoL modifications. It doesn't have any additional compatibility over the base image. It may happen to work in other machines, but that will be where the original IIsi ROM would also work. So it should be discarded for the sake of this discussion.
There's a few likely scenarios. It's hard to tell which without intimate debugging, though.
For the cards that boot straight into the 040 (CPU is not switchable), then there's a card ROM used to extend the stock ROM (which wouldn't know what to do when presented with a 68040). In some cases the approach taken is patching over parts the stock ROM, replacing code, so the "actual ROM" is a patchwork combination of data on the card and data on the romsimm. In this case when used with an unexpected ROM SIMM, the result is dog food and nothing will work.
Or, that ROM on the card may be trying to "gracefully" extend the stock ROM rather than outright patching it, which can be more tolerant to different ROM SIMMs, but the SE/30 ROM is ancient.
Or neither of those are the immediate issue, but perhaps the additional code on the card is unprepared to deal with the older hardware - this is what goes wrong with the Turbo 601, for example.
And finally, as
@alectrona2988 said there could be a gross hardware incompatibility such as not expecting to work with the slower bus clock.
It'd certainly be worth trying an IIci ROM image, though. I just verified it will boot a SE/30.