When trying to find the equivalent for beans created by any Spring XML parser, the first step is to look at the namespace handler, in this case MongoNamespaceHandler. Examining that class shows that the jmx namespace is parsed by the MongoJmxParser. Next step is to look at that and you'll see that it defines a bunch of beans; see here.
protected void registerJmxComponents(String mongoRefName, Element element, ParserContext parserContext) {
Object eleSource = parserContext.extractSource(element);
CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), eleSource);
createBeanDefEntry(AssertMetrics.class, compositeDef, mongoRefName, eleSource, parserContext);
createBeanDefEntry(BackgroundFlushingMetrics.class, compositeDef, mongoRefName, eleSource, parserContext);
createBeanDefEntry(BtreeIndexCounters.class, compositeDef, mongoRefName, eleSource, parserContext);
createBeanDefEntry(ConnectionMetrics.class, compositeDef, mongoRefName, eleSource, parserContext);
createBeanDefEntry(GlobalLockMetrics.class, compositeDef, mongoRefName, eleSource, parserContext);
createBeanDefEntry(MemoryMetrics.class, compositeDef, mongoRefName, eleSource, parserContext);
createBeanDefEntry(OperationCounters.class, compositeDef, mongoRefName, eleSource, parserContext);
createBeanDefEntry(ServerInfo.class, compositeDef, mongoRefName, eleSource, parserContext);
createBeanDefEntry(MongoAdmin.class, compositeDef, mongoRefName, eleSource, parserContext);
parserContext.registerComponent(compositeDef);
}