Yes, you commonly see luminosity quoted with two numbers: an occasional frequency range in keV/MeV/GeV and then a luminosity in erg/s. The use of two different energy units in one sentence is its own sort of eyebrow-raiser; Here is a bevy of recent examples, to prove that it's neither a sign of age nor a particularity of the LIGO group: , , , , , , , .
This course from nrao.edu states that "Most astrophysical theory is done in cgs units, but radio observations are usually reported in mks units since engineers use mks." (Here "mks" is an abbreviated SI system.) Maoz's Astrophysics in a Nutshell also seems to use cgs quoting erg/s, and this textbook claims that it just happens to be the most common in astrophysics.
What's really interesting is that I cannot find any astrophysical journals which require it, but two astrophysical standards organizations forbid it: IAU and AAS. So CGS is persisting in common practice despite institutional pressure rather than because of it.
CGS has persisted in astrophysics and continuum mechanics. The exact reasons are not 100% clear: however in both cases it is nice that it is within a few factors of 10 from the equivalent SI units, which allows you to quickly communicate to the engineers on the team what a wattage is if you have a power output in erg/s, so probably that is a huge factor. This reminds me of the eV unit where it is a compromise between the theorist's requirement that we never use Coulombs and the engineer's requirement that we use volts.
In the latter case of continuum mechanics, it's probably just because cgs gave nice names to viscosity properties, "poise" and "stokes". In the astrophysical case I am less certain, but it seems like it's probably just because occasionally theorists need the Maxwell equations and yet nobody really wants to be bothered by the permeability and permittivity of free space, these being highly unnecessary concepts created by the ubiquity of volts and amps.