ZLORIGIN and the gallery

I am aware that you cannot access the sims 4 gallery without a genuine base game. I have a genuine based game and a few expansions and game packs installed through regular origin, but if I was to download the rest through zl origin and then play my genuine based game, would the zlorigin packs still be there and I can still access the gallery?

Yes, you can have 1 folder where you combine genuine Origin, ZLOrigin and cracked versions of the Sims 4.
It all boils down to the labelling and use of the folder Game.

At present you only have genuine games installed.
Now make a copy of the folder Game and name it Game_Origin.
When you now update via ZLOrigin, again make a copy of the folder Game and name it Game_ZLOrigin.
If you want, you can also use a G4TW download for f.e. Toddler Stuff and name that Game folder to Game_cracked.

Now you can play any version via their own Game folder.

OK thank you. So if I had installed origin and zlorigin, when I play through the genuine origin with the packs I installed through zlorigin still show up and be usable in game?

No, when you play via genuine Origin only those games you actually bought will show up.
That's why you should use real Origin for downloading from the Gallery only.

With ZLOrigin you will of course have all DLC's.
With cracked games you'll have all DLC's that are represented by the latest crack, at present Toddler Stuff.

Note that when you play cracked games, the version will differ (1.33 still, whilst Origin/ZLOrigin have 1,35) which will result in the error "Unable to start, higher version, update via Origin".
You can solve that problem by copying the file Default.ini from Program Files\The Sims 4\Game_Origin\Bin to the Bin folder of Game_cracked.