The soil nailing is the mechanism by which your retained face is held up. Generally, whatever you put on the face of the nailed slope is there to prevent weathering of the exposed face and does not provide too much in the way of support. The shotcrete may offer structural support but only if it contains steel reinforcement.
You may need to contact a soil nailing company as they do tend to keep their design in-house and I would be surprised if you come across any design software on the market for such a specialised process.
If you are in the UK or if British Standards are acceptable on your contract, then you can design your soil nails in accordance with BS8006:1995 which approaches the design as a limit state philosophy.
A report has been written in Ground Engineering magazine July/August 1996 on the meeting held at the Institution of Civil Engineers, London on 10 April 1996 which may offer you some guidance.
Regards
Andy Machon
Andy@machona.freeserve.co.uk