I don't have much to add, but here's some facts & speculation --
Zimba / Zimba's was open 1969 to 1972 at 44 W. Commercial Row in Reno.
This property later became Old Reno Casino.

I was never in Zimba's, but did go into Old Reno Casino. It was mostly a long bar with some slots and very few table games. A small hole-in-the-wall place. They wouldn't have needed many chips to run the operation, IMO.

The Harvey Fuller Index shows 4 types of table games at Zimba's that would have used chips: 21, Craps, Roulette and Poker.

I think the Zimba (no 's) chips were first issue, as you show. However, the black no-denomination Zimba's with horseshoe mold doesn't belong to the first issues, IMO. (I can't guess what is WAS used for, however.)

Regarding the Zimba set of chips, the 10c and possibly 25c chips were probably used for low-limit craps. The $1 and $5 used on all the games, including $1 minimum blackjack. To pay off $1 blackjacks, they would have needed the 25c chips, or used regular half-dollars. As to why no first-issue $25 chips, it does seem they would need them, but they haven't surfaced. The only other (very speculative) explanation is that, with low limit games, they didn't really need chips higher than $5, unless a hot player needed to color-up before cashing out, in which case, the $100 black chip would be used. I think this explanation is unlikely, however ... just tossing it out.

All the Zimba's (with the 's) are second issues. Still using 10c chips for low limit craps. Now a 50c chip added for use on BJ payouts on $1 tables. Again, the $1 and $5's used on all the tables, and $25's for higher limit play and coloring up. As a low-limit place, they probably saw no need for new $100's. (Again, just my opinion.)

The green Zimba's "Z" chip seems to be a Roulette all right, consistent with listing a licensed roulette game. Why haven't other colors surfaced? I have no idea, but the rules for chip destruction were less rigorous back then, so the additional colors may have gone home with the former owners.

One final thought -- I haven't checked back issues of Doug Saito's Chip Chat, but he may have write-ups on Zimba's in some of his issues or auctions. If you're looking to research further, he may have some additional information about Zimba's.