  Although not nearly as numerous as binaries with two white dwarfs, eccentric
neutron star-white dwarf (NS-WD) binaries are important gravitational-wave (GW)
sources for the next generation of space-based detectors sensitive to low
frequency waves. Here we investigate periastron precession in these sources as
a result of general relativistic, tidal, and rotational effects; such
precession is expected to be detectable for at least some of the detected
binaries of this type. Currently, two eccentric NS-WD binaries are known in the
galactic field, PSR J1141-6545 and PSR B2303+46, both of which have orbits too
wide to be relevant in their current state to GW observations. However,
population synthesis studies predict the existence of a significant Galactic
population of such systems. Though small in most of these systems, we find that
tidally induced periastron precession becomes important when tides contribute
to more than 3% of the total precession rate. For these systems, accounting for
tides when analyzing periastron precession rate measurements can improve
estimates of the WD component mass inferred and, in some cases, will prevent us
from misclassifying the object. However, such systems are rare due to rapid
orbital decay. To aid the inclusion of tidal effects when using periastron
precession as a mass measurement tool, we derive a function that relates the WD
radius and periastron precession constant to the WD mass.
