You're right, there has not been rigorous testing of the Wii with ICDs. The ICD manufacturing company can likely give you the best information on that specific model. If the patient received the ICD very recently (less than 8 weeks), there is a valid concern that swinging a Wii controller around could dislodge the ICD leads and cause damage. If the ICD is older however, this is less of a concern.
It is unlikely that the electromagnetic interference from a Wii system would interfere with the ICD, so using a Wii should be fine. It is best to be in continued discussions with the patient's doctor as new evidence surfaces regarding ICDs and Wii.
Best of luck.
I'm really interested in this topic.
I had a PM/ICD implanted August 2009 due to Polymorphic VT - (no cause found yet) and I've done my Wii and PS3 and haven't noticed anything with mine - but I do stay 5-7ft away from it at all times.
What I found interesting is, the conveyor belt systems/registers at Target affect me and make my HR race but no other store has this effect.