I think I see what you're trying to say now. But impetui should be impetus to agree with veri, or veri should be vero (dative~genitive). It's also not clear what the subject of the main clause is: at a first read I assume it's unstated, so '(it/he) can hold back nothing of a true atatck/vigour' (in which case veri is correct); at a second read I take nihil as the subject, and have 'nothing can hold (him) back from a true attack/vigour', (in which case impetui is right), though I'm not sure dative of separation with retineo is a standard construction.
What's odd about the first line is that you have the perfect participle agreeing with its two subjects before the second subject, with its et, is introduced, and the absence of the esse obscures the fact that confusae is the verb of the dum clause. Since it comes before the et, my mind wants to construe it with virtus or mens or something, which is of course impossible.
In any case, since you need to deal with the two issues of hominis and impetui veri, the couplet will need some rephrasing, and I'm sure the meaning will come out more clearly once that is done.