I would like to point out that at least 90% of the proteins and vitamins in food are broken down when cooked, and more than 60% of minerals are lost in the water during boiling. This of course doesn't matter for your snake but you don't get the nutrients you think you do just because of a diverse food range.

Thiamine is only really high in cereals and grains (why whole grain is healthy) and is only really useful in the metabolism of said cereals and grains (high is sugars and starch), it has other uses in the body but considering a human uses several thousand calories a day just sleeping (22W used by brain, 10-15w by muscles) and maintaining body temp (120w) vs a snake which probably needs only a couple of hundred calories per day as it doesn't regulate its body temp and when cold can slow its metabolism. It becomes clear how it can survive on rodents considering that if it hasn't eaten anything containing thiamine in 10 hours, 90% will have left its system (see references from previous post).