The sight reading gigs I have done I was offered tab or proper dots, the MD would print the score off , the software allowed for either. I chose dots as I could use the experience to help with sight reading on other ( none string) instruments.
Just sounds like he can only read tab and isn't comfortable with dots.
If I was teaching I'd buy a cheap practice amp off eBay for my students to use. A ten second look on eBay revealed a new 20w amp £25 delivered plus many others.