Passing usb data traces underneath of DCDC converter
I suggest a good ground barrier between any signals near the DC-DC converter unless you are expert electromagnetic coupling design for PCB   The unknown is mutual inductance and the capacitance between DC pulse and USB transition current lines.

This means ground planes and guard tracks are necessary.
The ground barrier diverts E-field noise along with Gnd guard tracks for co-planar de-coupling noises. Controlled Impedance is needed above USB 1. 

You have 3 choices;    

1) Model it with Maxwell EMC software or crosstalk from lumped circuit model using Saturn PCB Toolkit   

2) Breadboard it or make a prototype and measure phase jitter margin in picoseconds on USB2  or USB3  error rate.   

3) Do nothing, cross your fingers and learn from experience about crosstalk on logic signals!

But this question begs the need for specs on Signal risetime and jitter tolerance and nearby crosstalk from supply rated at 150mVp-p @ 20MHz

Need your Specs

The transition current noise of a DCDC and its EMI noise will overlap with USB data spectrum up to 10MHz so that's like asking will it be quiet, if I live beside the train tracks, know the audio spectrum can interfere. 

The UART signals from 5V logic is 50 to 66 Ohms unbalanced ought to have controlled impedance and well-guarded on all sides (top/bot. and coplanar by ground signals and perfectly balanced to attenuate this. (CMRR using balun) 3.6V logic is 25 to 33 Ohms.