I have an eeprom dump (no .exe) of code that ran on an 80C188.. I've read IDA Pro can dis-assemble it (if 80286 real-mode is selected), but haven't had much luck getting it to work, so I want to try something else.

Any suggestions for a tool that will open a 80C188 .hex file?

The 80188 is mostly just a plain old 8086. You can use any 8086 disassembler. There are a few differences though:

new instructions: enter, leave, ins, insb, insw, outs, outsb, outsw, popa, popaw, pusha, pushaw, ud2

push immediate

shl, shr, rol, ror, rcl, rcr, sal, sar with immediate count

some new forms of imul