While it still isn't that common, land hermit crabs have definitely been bred in captivity before (see below):
A self-taught crab enthusiast is doing something remarkable — breeding land hermit crabs in her home.
theoutline.com
Even if they hadn't, it doesn't seem to be a prerequisite for an exhibit animal to be able to be bred in captivity to be included in the game. I don't think the goliath frog has ever been successfully bred in captivity before and nobody has ever seen the larvae of a titan beetle before, even in the wild.
If I had to choose twenty vivarium species for Planet Zoo, they would be:
1. Ocellated lizard
Timon lepidus (Near Threatened), Europe - Arid display
2. Psychedelic rock gecko
Cnemaspis psychedelica (Endangered), Asia - Tropical display
3. Veiled chameleon
Chamaeleo calyptratus (Least Concern), Asia - Tropical display
4. Saharan spinytail lizard
Uromastyx geyri (Near Threatened), Africa - Arid display
5. King cobra
Ophiophagus hannah (Vulnerable), Asia - Tropical display
6. Yellow lipped sea krait
Laticauda colubrina (Least Concern), Asia/Oceania - Aquatic display
7. Cuban boa
Chilabothrus angulifer (Near Threatened), Central America - Tropical display
8. Sinaloan milk snake
Lampropeltis triangulum sinaloae (Least Concern), North America - Arid display
9. Pancake tortoise
Malacochersus tornieri (Critically Endangered), Africa - Arid display
10. Panamanian golden frog
Atelopus zeteki (Critically Endangered), Central America - Tropical display
11. Kihansi spray toad
Nectophrynoides asperginis (Extinct in the Wild), Africa - Tropical display
12. Yellow spotted climbing toad
Rentapia hosii (Least Concern), Asia - Tropical display
13. Sonoran Desert toad
Incilius alvarius (Least Concern), North America - Arid display
14. Emperor newt
Tylototriton shanjing (Vulnerable), Asia - Tropical display
15. Atlantic mudskipper
Periophthalmus barbarus (Least Concern), Africa - Aquatic display
16. Eastern lubber grasshopper
Romalea microptera (Least Concern), North America - Arid display
17. Giant riverine tiger beetle
Calochroa octonotata (Data Deficient), Asia - Arid display
18. Desertas wolf spider
Hogna ingens (Critically Endangered), Europe - Arid display
19. Seychelles giant millipede
Sechelleptus seychellarum (Endangered), Africa - Tropical display
20. Coconut crab
Birgus latro (Vulnerable), Africa/Asia/Oceania - Tropical display