Saluē! immō means "to the contrary," and uērō in such a position tends to mean "but" or "however," though it can also mean "truly" depending upon the context. I have the 6th edition of Wheelock, yet I can't seem to find the passage you cite; the 8th of the Loci Antiqui is called "Hannibal; the Second Punic War" in my book. If you gave the full sentence, it would be easier to tell the exact meaning.
immo vero is a set phrase that can usually be translated "quite the contrary". Lucus is quite right: immo means "on the contrary" and it is strengthened here by the adverb vero. This phrase is not from Loci Antiqui but from Loci Immutati 8.
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae