Since the rocks are NOT glued, you can keep them on there--I actually recommend it.

NON-glued rocks or pebbles are often put on top to dissuade pests from getting inside of the soil. You can see pebbles and rocks at nurseries labeled 'top dressing'. Anything thats glued should ALWAYS go. Not glued is alright. : ) Make sure this plant is in a brightlly light spot with good airflow, and occasionally pick up the rocks and wash them with soap. This will completely prevent mold becoming on the rocks.

I'm not a fan of top-dressing plants unless they're being prepared for a show, or unless your soil is inordinately fast-drying, so I'd scrape them off and replace (if necessary) with a medium that has the same drainage characteristics as the main body of soil. There is a lot of advantage in using media that dries out quickly, as opposed to media that tends to remain soggy for extended periods. If your indoor trees are able to go more than 3 days w/o water, it's a pretty sure bet you're losing potential to excess water retention. Removing the top dress will hasten evaporative water loss and reduce the likelihood of limitations associated with soils that stay soggy too long.

IF you decide to keep the rocks and you DO wash them occasionally, make very sure you rinse thoroughly. Soaps/detergents and roots don't mix well as the lipid membrane surrounding the fine rootage can quickly be dissolved with disastrous results following for the root.

Al