This is of coarse a hypothetical question cause I do know that he needed to make the old ones reappear in order to do the thing with Cell. But this is only part of the question if Dende created new balls would the seven Dragons appear? I think not because there should be no negative energy in the new balls but im curious.
I don't think there is an "official" answer to this question as technically GT is anime-based only (Toriyama did not make the whole story himself), but a fair guess would be that it is irrelevant - the seven dragons would appear as long as enough wishes were asked of from Shenron. According to the anime, the only important factor (other than the content of the wish itself) that influenced and kept the dragons from appearing was the time lapse between successive wishes, which was dramatically reduced after Bulma invented the dragon radar.
Of course, there are all sorts of fan-based speculations as to why the dragon balls weren't simply kept in the hyperbolic time chamber after every wish (since it is quite possible to catch the balls after a wish before they are dispersed, as was once done by Goku) so that the negative energy would dissipate, but they are just theories.
It would take longer, but they would appear eventually. Humans would keep on wishing for stuff, adding to the negative energy stored in the balls. So I guess they could renew the balls from time to time, preventing the negative energy from building up, but where would the energy go and what would happen to the balls? The negative energy is still around, so I think even if the balls would be renewed over and over again, the cumulative negative energy would eventually make the seven dragons appear. I think it was Earth's destiny for it to happen. We should all be happy that at that exact time, Goku was coincidentally strong enough to defeat them. Imagine what would have happened if he was still only a boy.