Sure you can flash an EI22 ROM once rooted and on EL30. You will have the EL30 modem with an EI22.. A hybrid or mix if you will...
When you do a full wipe in CWM and flash a ROM you are basically overwriting the entire OS, so the only thing being left behind is the modem in this case.
Next question just in case, you can then go from EI22 ROM rooted back to an EL30 based ROM.