I've used the 1st ed Players Guide in a campaign of 2nd ed W:TA.
You'll have to decide if you want to include all the extra complications to char gen which the Players Guide (PG) has and 2nd ed WTA doesn't. Namely
- merits & flaws
- personality archetypes
- planetary aspects
Including them just makes the whole process more fiddly, and you'll need the 4 page version of the tribal character sheets to record it all. Also, be aware that there are additional merits & flaws in other sourcebooks. (I had a player who drove me bonkers asking questions about merits which were in books I didn't own). Personally, if I ran WTA again, I would ban the lot of them as too much book-keeping for the GM and too many contradictory character traits for the players to keep track of. But perhaps that's just my players :-)
There are also lots of extra gifts in the PG which aren't in 2e core rules. In the end I typed myself a list of all the relevant gifts (UK campaign, so US tribes were irrelevant) from the 2e core rules, PG and tribe books, so the players didn't have to look thru several books when choosing. Or at least knew what book and what page number. Some kind person has now put a much better, full list on the web:Wyrmfoe's gift list
The stuff on tribes and other shapeshifters in the PG has mostly been duplicated or expanded on in the various tribe/breed books. IIRC the Gifts are sometimes an exception to this - the PG might have some which are not in any other book.
