Ushanas is the name of a Vedic rishi with the patronymic Kavya (descendant of Kavi) as mentioned in Atharva veda ,who was later in puranas is been identified as Ushanas Shukra.
- Ye, Mitra, Varuna, who help Trisoka, Medhātithi, and Usanā son of Kavi.
In vedas sage Brihaspati is often referred variously as Vakpati i.e. (lord of speech) and is called as the Brahman. And also at some places as Purohita of gods in Shatapatha Brahmana. Sage Brihaspati is son of Angiras son of Brahmadeva.
- And on the following day, he goes to the house of the Purohita (the king's court chaplain), and prepares a pap for Bṛhaspati; for
Bṛhaspati is the Purohita of the gods.
In Rig Veda Brihaspati is also a deity of wisdom and is who that kills the asuras.
Now your question is whether both of these are same or not and you are quoting Seer among the seers.(कविं कवीनामुपमश्रवस्तमम &, कवीनामुशना कविः )
First of let us understand that here the word Kavi is used in two different contexts and is having totally different meaning. Krishna in BG is refering the rishi Kavya Usanas whereas in RigVeda the word Kavi is used to denote highest seer or sage (kavi) which is addressed to Brahmanaspati and is in the context of wisdom or Vidya (knowledge) . So there no direct relation between Brihaspati and Usana.
Now even the later scriptures like Mahabharata and puranas is conforming the above ,so let's see some of them.
In Mahabharata Section CCXLIX we find that both Usanas and Brihaspat are different personalities as it is mentioning that daityas learned the mantra vidya told by Usanas and Brihaspati both .
Meanwhile the fierce Daityas and the Danavas who had been defeated of
old by the celestials and had been dwelling in the nether regions
having ascertained Duryodhana's purpose and knowing that if the king
died their party would be weakened, commenced a sacrifice with fire
for summoning Duryodhana to their presence. And mantra knowing
persons then commenced with the help of formulae declared by
Brihaspati and Usanas, those rites that are indicated in the Atharva
Veda and the Upanishads and which are capable of being achieved by
mantras and prayers.
Also in Mahabharata Shukracharya is called as usanas who is the the son of Kavi as widely known from other scriptures as well.
But Devayani, with eyes red with anger, would not desist. Speaking not
a word to the king, with eyes bathed in tears, she soon reached the
side of her father Usanas, the son of Kavi.
So Rishi usanas is called as Kavya Usanas as his fathers name is prefixed before him and that indicate his father and this word kavya is not interpreted as poet as such.
In Padma Purana
vol. 4 -Chapter 3 -Various Mountains and regions of the world - Verses - 31b-41a The Kavi Usanas is identified with Shukra and is said to be honored by demons on mount Meru.
On the summit of that mountain only Usanas or Kavi (i.e sukra ) is
honoured by the demons
But interestingly there is some connection between shukracharya and Brihaspati because of that it appears that both are the same but in fact not. Let us see.
As mentioned in Matsya Purana-Chapter 47-Verses 182-184. - Brihaspati took guise of Sukra and lead the asuras in war.
Once Shukracharya for benefit of his wife jayanti and to please her had engaged with her for ten years. i.e. was sporting with her. At that time asuras were without guru or a wise leader. Knowing this Brihaspati , from the inspiration of Indra took guise of Sukracharya. I.e. he he took the form of Sukracharya.
बृहस्पतिस्तु संरुद्धं काव्यं ज्ञात्वावरेणतु।
दशवर्षाणि जयन्त्या हितकाम्यया।। 47.182 ।।
ततस्तानागतान् द्रृष्ट्वा बृहस्पतिरुवाचह।
स्वागतं मम याज्यानां प्राप्तोऽहंवो हितायच।। 47.184।।
When Brihaspati came to know that Shukracharya , for the benefit of
Jayanti and to please her , had been bound on a bondage for ten years
in order to please her , then taking it as the biggest shortcoming of
the daityas ,at the inspiration of Indra , he took to the form of
Sukracharya and summoned the asuras. On the arrival of the daityas ,
Brhaspati (in the form of sukra) spoke to them " O my clients , you
are welcome. I have returned from the tapovana for the sake of your
So in conclusion both of these figures Kavya Usanas and Brihaspati are different. In Rig Veda Sage Brihaspati is called as " Kavim Kavinaam " as Bṛhaspati was a deep thinker and one who had firm convictions in many matters. He was a man of vast knowledge. Every move of the devas against asuras had its origin in the mind of Bṛhaspati. There is no philosophy which does not contain the exhortations made by Bhaspati at various times to the devas (gods) or kings or hermits. And is referring to sage Bṛhaspati . Krishna On the other hand in BG is referring to Kavya Usanas "कवीनामुशना कविः - Kavina Usana Kavihi" I.e.Usana the son of Kavi.I.e. kavya Usanas. So even though both the quotes are saying the similar thing i.e. Seer among seers , but they are not referring to same persons.