does the 2020 unemployment tax exclusion reduce adjusted gross income for the student loan caculation

No.  There are some other discussions here about how the "conforming amendments" in the new law told us not to change those.  

Because that is the way the law says to do it:

(courtesy of TGB, Jensen, Bob and whoever else I missed).

The calculation for taxable Social Security (and about 6 other things) still use the FULL amount of unemployment.  The $10,200 exclusion does NOT apply to those calculations.

These are the items that still use the full amount (thanks to "Judy" on another forum that I'm copy-and-pasting this):

• Taxable amount of social security
• Exclusion for US savings bond interest used for higher education
• Exclusion for employer-provided adoption assistance
• Limit on deductible IRA contributions by plan participants
• Limit on student loan interest deduction
• Limit on deduction for tuition and fees
• Limit on rental real estate exception to passive activity loss rules

For code-heads, these are Conformity Amendments for MAGI under Sec. 9042(b) of the ARP Act.