Greetings,
This is a practise which is followed by the industry giants since ages. Its not only limited to hiring them as consultant , but creating a Knowledgebase to ensure there is a exchange of information even if they are not available to be re-hired.
As per Ravi Arora, head of Knowledge Management at Tata Steel, "Future plans for KM at Tata Steel include linking e-learning with the KM repository and KM communities, devising an intellectual capital index, networking with retired employees, employee skill development for better externalization of knowledge, and integration with customer's knowledge".
Implementing Outreach Programs will be win win for everyone. The challenge lies in moderating the benefits to keep the employees and ex-employees motivated in the long run.
Here's a news published on Hindu
The Hindu : Opportunities / Miscellaneous : Firms see advantage in rehiring laid off staff
Wish you all the best !