Although it it true that the Emerald crab is normally added to a tank for algae control (especially bubble algae) they are omnivores. They can and will eat meat. They are part of a tank's CUC and that is exactly what they do. Given the opportunity, they will eat fish fry. As the eggs hatch and the fry head for parts unknown, they are at the mercy of the environment.
By the way, if you ever want to catch an Emerald crab all you need to do is place a grocery store shrimp in a clear glass and lean it against your live rock just before tank lights go out. Chances are very good you will find the crab in the glass eating the shrimp in the morning. He didn't go in there after algae.
I'm glad that you looked it up. The real key to success in this hobby is going slowly, researching as thoroughly as possible, asking folks on line to get opinions of those knowledgeable, making educated decisions, and resisting impulsive buying.
Watching what goes on in your tank is the most enjoyable part of the hobby. It is really neat to see the clowns lay eggs and guard the nest. I just wanted to make you aware that there is no chance of raising fry in your tank. That should not take away from your enjoyment at all. In the wild, the vast number of fry do not survive. That's why fish lay hundreds of eggs.