I don't think it will be harmful, but means that it was digested too quickly and passed through. Missed nutrients is probably the main result. BSFL are so small that they are usually eaten in large quantity and gobbled down pretty quickly by a dragon. If they don't take time to chew the BSFL, it may pass through undigested like this. While I don't think this is harmful, it might be best to hand feed the BSFL and slow the rate they're eating to allow for more thorough chewing when possible.