The short answer is yes.
Many other Qualification vendors use only Caffeine for Wavelength Accuracy, at 205nm and 273nm. Holmium oxide of course covers 241-641nm, and is directly traceable to NIST standards. However, if you want, there is no reason you could not simply take the spectrum of Caffeine as well.
The L3 Solution provides a nice, mid-range absorbance value, compatible with most UV-Vis Detectors. You could of course use any other concentration that gives a suitable response. The reference solution would be Mobile Phase, but there is very little difference if wanted wanted to use Water.