That is partially correct. Shri Shridhara Svaami had Vaishnava bias, though he was known to be a Smaarta. This is also why Shri Chaitanya Mahaprabhu is said to have accepted his commentary on the Bhaagavatam. For example, in his commentary on the Bhagavat Geeta, Adhyaaya 14, Shloka 27, he interprets the shloka as referring to Shri Krshna as the source of Brahman, which is a Gaudiya concept and not accepted by Smaartas.
NOTE: I disagree here with the Gaudiya views.
Coming to the Pancharaatra Aagamas, Shridhara Svaami did accept them as authoritative, though they were rejected by other Smaarta philosophers, including Shripaada Adi Shankaracharya himself. In his Bhaagavatam commentary, he says:
मयोदितेष्ववहितः स्वधर्मेषु मदाश्रयः वर्णाश्रमकुलाचारम् अकामात्मा समाचरेत् ” मया – पञ्चरात्राद्युक्तवैष्णवधर्मेषु, अवहितो अप्रमत्तः।
“Taking full shelter in Me, with the mind carefully fixed in the devotional service of the Lord as spoken by Me, one should live without personal desire and practice the social and occupational system called varṇāśrama.” Here, ‘devotional service spoken by me’ refers to the Vaishnava dharma explained in the pAncarAtra texts. ‘Fixed in such devotional service’ means to be attentive/careful.
-Srimad Bhagavatam 11.10.1
क्रियायोगेन शस्तेन नातिहिंस्रेण नित्यशः ” क्रियायोगेन – पाञ्चरात्राद्युक्तप्रकारेण
Meaning: “Without excessive violence, one should regularly perform one’s devotional activities.” Here, kriyA yoga means “by the method of worship enjoined in the pAncarAtra etc.”
If Sridhara Swamin had considered these Vaishnava Agamas as veda-bAhyas, he would not have said that exemplery devotees of the Lord follow the Vaishnava dharma of pA~ncarAtra diligently.
Sridhara Swamin also says that the Vishvaksena the commander of Lord’s army in Shri Vaikuntha, is the personification of the pA~ncarAtra tantra, just as Shri Garuda the Lord’s mount is the personification of the Vedas
-Srimad Bhagavatam 12.11.19-20
He also accepted the Pancharatra in Bhavarthadipika, 1.3.8.
Coming to Shri Amalananda, here's what he said in shAstra darpaNa and bhAmati kalpataru.
जीवाभिन्नब्रह्मणो जगत्सर्गं वदतः समन्वयस्य जीवोत्पत्तिप्रतिपादकपाञ्चरात्रस्मृतिविरोधसंदेहे, अधिष्ठातैवेश्वर इति मते निरस्ते, प्रकृतिरपि स इति मतस्य वेदसंमतत्वाज्जीवोत्पत्तावपि प्रमाणत्वम् — एवंभूतावान्तरसंगतिलोभेन स्मृत्पादसंगतमप्यधिकरणमिह लिखितम् । तत्र —
ईशोक्तं न पुराणेषु व्यामोहार्थमितीरितम् ।
पञ्चरात्रमतो जीवो विकार इति मीयते ॥
पञ्चरात्रकर्तुर्वासुदेवस्य वेदादेव सर्वज्ञत्वावगमात् कपिलपतञ्जल्यादीनां च जीवत्वात्, पञ्चरात्रस्य च पुराणेषु बुद्धादिदर्शनवत् व्यामोहार्थमीश्वरप्रणीतत्वाश्रवणात् ब्रह्मनिमित्तत्वप्रकृतित्वसंप्रतिपत्तेश्च जीवोत्पत्तावप्यद्वैताव्याघातात्तत्सिद्धजीवोत्पत्तिरबाध्या । अत एवागतार्था च । एवं प्राप्ते, अभिधीयते —
“बुद्धिपूर्वकृतिस्तन्त्रं ब्रह्मनिःश्वसितं श्रुतिः ।
तेन जीवजनिस्तत्र सिद्धा गौणी नियम्यते ॥”
यावद्ध्येकदेशे वेदाविरोधादीश्वरबुद्धेर्वेदमूलत्वं वेदाद्वा सर्वविषयत्वं प्रतीयते, तावदेव स्वतःप्रमाणवेदाज्जीवानुत्पत्तिप्रमितौ तादृशबुद्धिपूर्वकेश्वरवचनान्न जीवोत्पत्तिरवगन्तुं शक्यते । अतः प्रमाणापहृतविषये गौणं तद्वचनम्, न तु भ्रान्तं पूर्वोक्तयुक्तिभिरिति ।
Meaning: The adhikaraNa is begun as follows — there is a doubt as to whether the the origination of the individual soul (jIvotpatti) must be accepted literally from statements in the pAncarAtra Agama. This tantra was composed by the Omniscient Lord, and are in agreement with the Veda in terms of the oneness of material and efficient causes. It cannot be said that these statements are made in error, since they were uttered by the Lord Himself, compared to other darshanas like sAMkhya, yoga, etc. that were composed by jIvas like Kapila, Patanjali, etc. Moreover, we do not see anywhere in the Puranas that the pAncarAtra tantra was propagated by the Lord Himself for the sake of delusion not unlike the doctrine of the Bauddhas propagated again by Himself to delude the wicked. Such a doubt is raised here.
The correct position, on the other hand , is as follows: “Since the Lord’s voluntary composition is the pAncarAtra tantra, and His involuntary breath is the shruti, statements of origination of the soul are secondary and figurative, not primary and literal”. The omnscience, benevolent nature, and infalliability of the Lord are all understood to be true only from the self-evident shruti. Hence, the pAncarAtra Agamas are dependent on the Veda for their authority. Hence, it cannot be said that they propagate the theory of origin of the individual soul literally, since it would contradict the shruti that says the individual soul is eternal. Therefore, such statements in the pAncarAtra are to be understood as secondary and conveying something else, and are not erroneous due to the reasons given in the prima facie position.
Hope this helps.