Apart from both being blue, the iconography of the two Buddha's is completely different - different mudras and implements for example. Their "function" is also different. One represents wisdom (Akṣobhya) and the other compassion (Bhaiṣajyaguru). if they are supposedly the same, then why are they so different?
This post on Dharma Wheel says that, at least in Japan, Aksobhya was venerated the same as the Medicine Buddha (i.e. as the Buddha to appeal to for dealing with this worldly medical problems) until news of Bhaisajyaguru's sutras arrived in Japan.
In any case, Shakyamuni is often described as a doctor and the Dharma as a diagnosis and prescription for what ails us.
Depends on which dimension of reality one talks about. From the mundane dimension, both Bhaisajyaguru and Aksobhya are Buddhas of the Eastern Pure Lands. And according to the Amitabha Sutra, there're countless Eastern Pure Lands Buddhas:
..."Śāriputra, thus do I now praise and extoll the inconceivable merit of Amitābha Buddha. In the East there are also Akṣobhya Buddha, Appearance of Sumeru Buddha, Great Sumeru Buddha, Radiance of Sumeru Buddha, Wondrous Sound Buddha, and thusly as many buddhas as there are sand grains in the Ganges River...
Then from a supramundane dimension, all Buddhas have transcended all wrong views (not-I), all cravings (not-mine), and all conceits (not-myself) ( ~~AN 3.32 ~~ ) and as a result, all notion of sameness or difference no longer applies.