ξυμφέρει
σωφρονεῖν ὑπὸ στένει.
τίς δὲ μηδὲν ἐν δέει
καρδίαν <ἂν> ἀνατρέφων
ἢ πόλις βροτός θ᾽ ὁμοί-
ως ἔτ᾽ ἂν σέβοι δίκαν;
Eum. 520-525

is "an" with the participle always used for the present optative or the imperfect indicative? It seems that, in this example, it is being used with a conditional participle; hence, "if nurturing a heart not all in fear, who, either city or mortal man, would still revere justice likewise?" I don't understand how you could translate "an" with the participle as a separate question.

A sharp observation. This way we have here two (optative or indicative doesn't matter) potential sentences, while we should have the condition of σέβοι with an εἰ implied by our participle. Notice Wilamowitz : τίς δὲ μηδὲν ἐν φάει καρδίαν ἀνατρέφων ἢ πόλις βροτός θ' ὁμοίως ἔτ᾽ ἂν σέβοι δίκαν. I think that the editor of your text may be wrong to propose ἂν as addendum.

I think so too. I do not think it is possible to derive a logical translation if you add ἂν.