Interestingly enough, on that caps0ff site, there are several Raiden II chips that have yet to be decapped. What do those chips do, then?
I believe most Seibu custom chips are gate arrays, not MCUs. The only ones known to have internal ROMs are the T5182 sound CPU found on their later 8-bit games and the undumped graphics SIPs on Air Raid/Cross Shooter (and presumably also Yukai Tsukai).
> QFP Raiden 2 SEI360
This is presumably part of the later edition of Seibu's 16-bit tilemap hardware (though Zero Team curiously lacks any equivalent chip). Earlier Seibu games use SEI0210 and SEI0211.
> QFP Raiden 2 SEI1000
This is the second version of the notorious COP DMA/math chip. Most 68K Seibu hardware games have SEI300 instead, but no meaningful differences are known.
> QFP Raiden 2 SEI252
Encrypted sprite chip for Raiden II and the first few SPI games. Preceded by SEI251 on Zero Team; succeeded by RISE10 and RISE11, the latter of which remained in use until Seibu stopped making arcade games.
> QFP Raiden 2 SIE150
QFP successor to the SEI0100BU sound interface.
> QFP Raiden 2 SEI0200
Also video-related; this probably provides the "CRTC" functionality which the MAME device of that name only partially emulates.