Are these resistors in parallel?
No, R1 and R2 are not in parallel unless the load was 0 Ω (so vout = 0).

Assuming the load is non-zero, but it is not a simple resistive load that can be separately measured, you can get an equivalent resistance by measuring the current through the load and the voltage across it.

$$R_{load} = \frac{vout}{I_{load}}$$

Then, the resistance from the junction of R1 and R2 to ground would be:

$$R_{parallel} = \frac{R1 + R2 + R_{load}}{R1 \times (R2 + R_{load})}$$

Note that if you plug in 0 for \$R_{load}\$ in the above equation, you get the formula for just R1 and R2 in parallel, as stated in the first paragraph.