does google count it as 'reciprocal'?
 

say you have two different domains on the same shared host, domain A & B

now you have another two different domains on a different shared host but hosted together, domains C & D


if A links to C and D links to A, does google consider that as reciprocal?

It does count,you can have up to 25 domains on one ip and do mutual link exchange.

I agree with "it does count" part...

but where is the source of the number you came up with?

according to Matt Cutts you shouldn't be bothered with IP addresses and amount of servers - unless you are talking about a few hundred sites... Google is aware of the fact that lots of people use shared hosting for legitimate reasons.