If a unit had multiple ways to receive an order in a single round, like Death Troopers via Entourage and a command card (e.g Covert Observation), are they able to use comm Relay multiple times if equipped?

A unit can only ever be assigned 1 order in the command phase. If it is assigned an order via entourage it is no longer eligible to recieve an order from a command card (or any other source).

This rule functions even if the first order is transferred via comms relay.

KommanderKeldoth already answered it, but you can find the official rule in page 53 of the RRG, the last dot under "Issuing orders".

"During the Command Phase, a unit can be issued an order only once, even if a game effect causes that order to be removed or issued to another unit instead."