Help understanding onboard power supply measurement test connections
Your scope should have a capacitor in series to block DC when making AC measurements. Putting a blocking capacitor in the test circuit would be redundant, and also would prevent you from monitoring the DC voltage (which might be useful for certain tests).  

The reason for R133 being 49.9 Ohms instead of 50 Ohms is simply that 49.9 is the nearest value in the E96 1% resistor series.

You are probably right about the purpose of R134. 

R137 compensates for the combined resistance of R135 + R134, which would otherwise make the output voltage about 1% too high (it would not be needed if R135 was 3115 Ohms, but that is not a standard value).