For the most part, Yes.
You can write:
let vTest = 'sum(Amount)';
set vTest = sum(Amount);
they are both evaluated when your write $(vTest) in your application.
I'm more unsure of the syntax:
Set vTest = =sum(Amount)
As far as i know, writing:
Let vTest = '=sum(Amount)';
will not give the same results.
What are you trying to achieve and why would you want to do this?
The simple answer to this would be no.
The LET statement evaluates the expression on the right side of the '=' before it is assigned to the variable, the SET will assign the text on the right hand side of the '='.
SET V1 = 1+2; Returns 1+2
SET V2 = 1+3; Returns 3
LET and SET are different when you define any value in the SET it treat as string and what ever we write it is string. But if ay assigning in the LET its value calculate and assign to the variable.
SET vNowSet = 'NOW()'; //This gives NOW()
LET vNowLet = $(vNowSet); //This gives Current date and time value