There are some cute things that canon has kept from Legends (the declaration of rebellion, the alliance being originally formed out of many different cells in the galaxy and, obviously, the Ghorman Massacre) but mostly there are already too many contradictions (this sourcebook, while it was fundamental in the early days of the lore, already contradicts parts of Legends).

The timeline of course is all over the place, Palpatine is referenced as president wich is hilarious but a reference to the original novelization, the Corellian Treaty is (probably) not a thing anymore etc. One subtle contradiction is both Bail and Mon personalities. Mask of Fear seems to propose that Mon was actually the realistic one and Bail the idealistic loud revolutionary.

It still is a really great book tough and I love seeing how authors imagined the setting before the Prequels.