Hardly. But it depends on who is on board.
Corruption exists everywhere. Do you think that Vukic was less corrupt? I am pretty certain you will find many people in Serbia who want to fix the country. Other Europeans would ask: why let only poor countries join? They drain money from richer countries. Switzerland and Norway will never join and they know why. Hint: there is a reason they are rich. Second hint: they got rich without the EU.
Which country got rich with the EU? I don't know of a single one. Germany was already wealthy before the EU was founded. France is now in debt crisis from which it can not escape, so it will drag the whole EU down.