Variability in White Dwarfs (physics and Sample Selection)

Continuing on with my exploration of 'what variability in Gaia DR2 can do', I looked
at the Warwick GDR2 WD sample; variability == sqrt(phot_g_n_obs)/phot_g_mean_flux_over_error .
I restricted the following to G<18, as there the expected "shot-noise" contribution to this definition of variability is < 0.02mag.

If one looks at the WD sample, one sees that variability is very non-uniformly spread across the CMD, in good part as expected:

 or with larger dots

If I split the sample into a "non-variable" and variable" one, I get the following density maps.

Non-variable

and variable

I (as an absolute WD amateur) see three things:
-- variability is great to eliminate contaminants among faint (M=13) red (BP-RP~1.3) WDs
-- DAV (ZZ Ceti) stick out nicely, of course
-- are the hot variable WDs DBV stars??

Is any of that known (in this prettyness), is any of it interesting?