While Teppan Edo might not be the same as a local teppanyaki restaurant, have you been able to get up and leave part way through dinner at TE to view IllumiNations or know if this is a common occurrence? I cannot imagine they would like this since it is a group seating and dining experience where the Chef cooks for every one at the table. The flow of guests is based on everyone finishing at about the same time so the next set of 8 guests can be seated.
It would be more likely, but not certain, that they would delay seating until after IllumiNations, but only if the restaurant is still open or willing to seat someone 45 minutes late. If it is an evening when the closing time is listed as 9 PM they probably would not seat after fireworks.
Waiting until the night of the reservation to see whether TE will accommodate the OP's desire to see IllumiNations and also have dinner would be a last resort because the restaurant could easily say no and then the OP would have to decide which is more important. If the OP wants to do both it would be better to keep looking for an earlier reservation or a later one if TE is open until 9:30.