«وَإِنَّ صَخْرًا لَتَأْتَمُّ الْهُدَاةُ بِهِ»
Indeed, Ṣakhr is someone whom even guides follow.
The central praise is already present: Ṣakhr serves as an exemplar of guidance, even to those who guide others. The rest of the line enhances this completed idea through a vivid image.
In taʾtammu al-hudātu bihi, al-hudāt is the subject and bihi a prepositional complement of the verb. The wording makes the concept of exemplary guidance explicit.