In the BG, the 11th chapter is called the Vishwarupa adhyaya. Therein occurs this verse:
ब्रह्माणमीशं कमलासनस्थमृषींश्च सर्वानुरगांश्च दिव्यान् ॥ १५ ॥ 11.15
ब्रह्माणं चतुर्मुखम् ईशम् ईशितारं प्रजानां कमलासनस्थं पृथिवीपद्ममध्ये मेरुकर्णिकासनस्थमित्यर्थः,
brahmānam, Brahma, with four faces; īśam, the Ruler of creatures; kamalāsana-stham, sitting on a lotus seat, i.e. sitting on Mount Meru which forms the pericarp of the lotus that is the earth;
The other Advaitin commentaries/glosses too give the same meaning as above.
While Shankara does not say anything about Shiva, even for the word 'īśa' of the words, Ramanuja and Madhwa say that Shiva is there:
Ramanuja:
ब्रह्माणं चतुर्मुखम् अण्डाधिपतिम् | तथा ईशं कमलासनस्थं कमलासने ब्रह्मणि स्थितम् ईशं तन्मते अवस्थितं
English translation by Swami Ādidevananda:
Brahma, the four-faced ruler of the cosmic egg. So too Siva (Isa) who is seated in the lotus-seated Brahma, meaning that Siva abides by the directions of Brahma.
Madhwa:
कमलासने ब्रह्मणि स्थितं रुद्रम् - 'विष्णुं समाश्रितो ब्रह्मा ब्रह्मणोङ्कगतो हरः ।
हरस्याङ्गविशेषेषु देवाः सर्वेपि संस्थिताः'' ॥ इति पाद्मे ॥१५ ॥
Madhwa cites a Padma (purana?) verse to say that: Brahmā resorts/relies/dependent on Vishnu, Hara (Shiva) is on the lap of Brahmā. In the various body parts of Shiva all other deva-s reside.
In the same chapter occur these other references to the term 'Rudra'
पश्यादित्यान्वसून्रुद्रानश्विनौ मरुतस्तथा । 11.6
Shankara says: पश्य आदित्यान् द्वादश, (12 Aditya-s) वसून् अष्टौ, (8 Vasu-s) रुद्रान् एकादश, The 11 Rudra-s (not Shiva)
रुद्रादित्या वसवो 11,22
Shankara says: रुद्रादित्याः वसवो ये च साध्याः रुद्रादयः गणाः These belong to the 'gaṇa' category.
Om Tat Sat