It's more like, there are plenty of really early old games that were coded to run on stock 68000 CPUs, and not be accelerated. Sometimes they break, and sometimes they just play way too fast (e.g. Ultima IV).
Nah... If it was coded for a 68020 then I would say it works on a 68030 just fine. By the time people started coding for the 68020 they were probably already thinking of coding it right.
... especially timing-wise since the 020 was available at various clock speeds, making simple cpu loops for timing delays (as common in typical 68000-at-7Mhz-only code) impossible.