Bad news:
with the card installed the SE/30 boots normally but doesn't show anything on the (white) screen.
After that I connected an Apple Studio Display 15" (M4551 rev. B ) (b/w) VGA with 3 different adapters, but the Studio Display tells me "signal not showable" or "no computer signal". SE/30 screen remains white.
Card faulty?
***
20 mins later:
same results with a second old (LCD) monitor - no CRT monitor available.
I think I'll remove the card and look if the SE/30 wants to show me his normal screen again.