Mini vMac is version/ROM specific. Since zydeco's version is a port, it may only support the Mac Plus 128K ROM (as I believe he would need to port each version separately). The ROM you downloaded may not be the 128K ROM, or may have a bad checksum. I've run into to that.
Your Mac Classic ROM will work with the Mac Classic version of Mini vMac, however, it is unlikely that zydeco's iPhone port will work with it. Use it with the standard desktop version of MvM/Classic though as you can even boot into the embedded System disk in the ROM (Cmnd+opt+X+O).
Might be worth zydeco doing a port of the Classic emulation for this reason alone, comes with it's own boot disk!