Can Arjuna's statements in Bhagavad Gita be taken as pramAna i.e., are they on par with Krishna’s?
Yes. All ancient Vaidika commentators take that as a pramana and for good reasons that I will explain.
Arjuna was worthy enough to receive the teachings of the Gita personally. To not believe him is equivalent to rejecting the Gita itself.
He is also re-iterating to Krishna the beliefs that were common during his time and even before: that the caste system is birth-based. Arjuna's claim is made by other reputable people in the Mahabharata like Yudhishthira, Bhishma, etc.
Bhishma, the speaker of the auspicious Vishnu Sahasranama, says the same thing:
...by uniting themselves with women of other castes, led not by considerations of righteousness but by uncontrolled lust, cause numerous mixed castes to come into existence whose occupations and abodes depend on the circumstances connected with the irregular unions to which they owe their origin.
Moreover, this claim is made by the Vedas themselves, and Jaimini has even written a sutra for it in the Purva Mimamsa Sutras, which are also commented upon by Shabara:
The Vedic verse is:
"We do not know if we are Brahmanas or non-Brahmanas ... Therefore, When the pravaras [ancestral lineages] are being recounted, one should say the deities are our ancestors- (Maitrayaniya Samhita 1.4.11 of the Krishna Yajur Veda).
The Vedic verse shows that the castes are based on ancestry (gotra), and hence, birth-based. If caste wasn't based on ancestry, then it would be useless to mention pravaras in that verse in relation to caste.
The Mimamsa Sutra for that verse is:
On account of the failings of women, (there can be no certainty regarding one's caste); specially as the son belongs to the progenitor. - Adhyaya 1, Pada 2, Sutra 13
And Shabara's commentary:
It is difficult to know if one is really a Brahmana; - and this is what is figuratively spoken of as "we do not know", and the difficulty in knowing it for certain is due to "the failings of women", and also to the fact that "the son belongs to the progenitor"; this is also indicated by the advice "May you guard this dynastic line with great care." - Apastamba Dharma Sutra 220.127.116.11
Now to reject Arjuna's statements as apramana, is to reject authorities like Arjuna himself, the honorable recipient of the Gita, Shabara, Jaimini, the Pandavas, the Mahabharata, Bhishma, Vishnu Sahasranama, Krishna, and even the Vedas themselves.
This is to be expected from neo-Vedantins anyways, since they are after all, unorthodox.