I've only had my pearls a few months and they haven't spawned yet, but in the past I've had honey gouramis which did spawn.
With honeys, the eggs are not easy to see, but they do make the bubble nest look different. It's hard to explain, the eggs when just laid are transparent and they look like tiny clear beads amongst the bubbles. They darken as the embryos start to develop. I assume pearls will be similar.