let's say ardus with dimodian.

If he is flanked - does he reroll on attacks or not? I am not native speaker, maybe not a careful reader, but I am not sure about it.

I know that flanked unit does not reroll for back ranks, bu is precise to be treated likewise?

Yes, that is the conclusion from a literal reading of the rules. Precise says that the unit is treated as having X additional ranks. Flanking prevents re-rolls from additional ranks...