No, I'm not an expert, but I've seen plenty of artifacts that are made from both fossil ivory and modern ivory. They simply don't look alike, not even to a casual glance.

How many exampes of both have you seen, in person?

I won't dispute that fossil ivory could possibly be bleached to look like modern ivory (which would have no effect on the elephants or arguably a positive effect, since it would be eating some of the market for the modern stuff), or that modern ivory could be stained to look like fossil ivory (which would devalue it).

I just don't see any economic incentive to do either one.