yes !!! there is a promise by Him in the B.Gita and other authentic shastras that He accepts and reciprocates accordingly, the devotion of all His devotees either Radha or Shiva or any other.
Krishna as a devotee of Radha, however never reaches the level of Her devotion. Krishna in transcendental devotion of Radha can go upto "MODAN" Bhava/Rasa. Radha in devotion for Krishna reaches "MAADAN", higher than Krishna's "Modan" Bhava. Here one point is notable that Krishna reciprocates any devotee's "Bhava" with His "Rasa". So, the Vedic mantra is "Raso Vai Sah.". And, here at this point Radha becomes the supreme in devotion. Perhaps, Krishna has no Rasa to reciprocate for Radha's Maadan Bhava in devotion. Radha is considered to be at the top most level of devotion and servitude, "yatha braj-gopikanaam"- also declared by Lord Narada.
Nevertheless, in the seventh canto of Srimad Bhagavatam, He Himself says that His (marginal) devotees like Prahlad are more dear to Him than His transcendental and eternal devotees like Radha (His own soul) and Shiva (the topmost Vaishnava, the Rudra). There are infinite trillion universes, all of them have one brahma, one vishnu, one shiva, respectively. At this level of eternity all of them have equal importance in their respective universe. This is what Srimad Bhagvat Mahapuran has to say about krishna, as the supreme at chapter 14 of the eleventh canto in the " Udhava-Krishna" Samvad!!
Guru Nanak devji says in the Japji Saheb, "eka mayi jagat vyaayi teen chele parvan; ek sansari ek bhandari, ek laye divan." .
In the Bhagvatam tenth skand (canto) lord bramha visited dwarkadheesh where krishna resided expanding Himself with all His 16,108 wives. For the enlightenment of lord brahma krishna manifested before him all the brahmas of all the other universes. Our universe has brahma who has four heads and our lord shiva has five heads. The other universes have differently headed lord brahmas and lord shivas.
Lord shiva and lord vishnu have least difference in divinity at mundane level. Sri Brahma-Samahita says that if vishnu is the divine milk then shiva is a divine yogurt. They are supplementing each other at this level of divinity.
Gosvami Tuslipandit says in the Ayodhya-Kand thru the Valmiki-Ram samvad, "jag pekhan tum dekhanihare, hari-bidhi-sambhu nachavanihare."
The C.c.(Chaitanya charitamrit, madhya-lila, specially ch#20) by sril krishnadas kaviraj has all the answers. Vishnu is a divine medium which Krishna uses for different avatars for limited mundane pastimes, however, Krishna Himself is the avataree and not an avatar. Jayadev Pandit of the Geet-Govind fame, in his "Dashavatar-Stotram" has also revealed this eternal truth almost eight centuries back, at the beginning of the Bhakti-era.
All the three types of vishnus/mahavishnus (kaaran, garbhas, kshiras) are the personality expansions or purushavataras of Krishna, a.k.a. the Parmatama, the All-indwelling, the role reversible, "Prerak-Brahman" form of the "Bhokta-Brahman". During His different incarnations He takes use of His own expansions to descend to the mundane pastimes from eternal pastimes. If we study the C.C. we will accept this divine truth, there would be no room for sectarianism left on our material minds. yes, the c.c. is all about convincing and concluding the spiritual information/knowledge which we have acquired reading (ascendingly) different scripture.
lord shiva and lord vishnu have least difference in divinity at mundane level. Sri Brahma-Samahita says that if vishnu is divine milk then shiva is divine yogurt. "kshiram yatha dadhi vikar viseshyogat, sanjayate nahi tatah prithak asti hetoh; yah shambhutamapi tatha samupaiti karayad, govindam adipurusham tam aham bhajami." (S.B.S ch#5, ver#45).