Directly from the Big Game regs, page 9 http://fishandgame.idaho.gov/cms/hunt/rules/bg/info.pdf
In any hunt, including any-weapon seasons, it is
unlawful to pursue or kill big game animals:
• With any electronic device attached to, or incorporated
on, the firearm or scope.
I would think that you would get a ticket if you used a illuminated reticle.
Did you talk to an Enforecement Officer or just the people that answer the phones at the front desk?