You cannot pass 'ids' here, you need to pass the domain i.e. the search criteria and search_count will directly return the 'count', so no need to use 'len' function.

It should be like

domain=[]

u_count = self.pool.get('res.users').search_count(cr,uid,domain,context=context)

Here it will not count inactive users, for that you can do the following:

domain=[]

my_context=dict(self._context)

my_context.update({'active_test':False})

u_count = self.env['res.users'].with_context(my_context).search_count(domain)

Hope this helps