Yes of course, conversion efficiency from 3.7V to 3.3V can even be higher if you use a high-quality synchronous converter that can work with 0.2V of dropout.
Dropout voltage is the buzzword here. A single Li-Ion can go down to 3.4V, then you always have some cable and plug resistance. That means, if your GPS and ESP work as well with 2.8V as with 3.3V then it may be a good idea, but if you want a lot of margin for the converter and a stable 3.3V - then I´d go for a higher voltage battery.
Look into the conversion efficiency curves of a common step-down IC. Efficiency vs. input voltage is usually quite the same up to a ratio of 1:2.5 (by my gut feeling, please confirm with the part of your choice).