Your linked article reminded me of 3 unique relationships among various downtown LV casinos --
1. Common-ownership casinos offer a common players' club -- nothing new there. But downtown, some also share amenities. The Four Queens and Binion's are commonly owned by TLC Casino Enterprises (Terry Caudill). The Four Queens offers their guests the ability to use Binion's sky-pool on the 25th floor of the original Mint tower. Maybe some other sharing too.

2. Similarly, Circa / Golden Gate / The D are all owned by Derek & Greg Stevens. The small & older Golden Gate offers guests the opportunity to use Circa's "Stadium Swim", with some limitations. But for budget-minded guests, you could stay at Golden Gate and use the Circa pool without paying top-dollar for Circa room prices. You would need to schlep between the 2 properties in your wet bathing suit & towel however! So ... maybe not.

3. For older chip collectors, turn back the clock 31 years to 1995, when the Fremont Street Experience opened. To commemorate, 10 downtown casinos got together and issued $5 "Fremont Street Experience - Grand Opening" chips from those 10 different properties. You had to visit 10 different cashiers cages to get them at face value (= $50 total). It was the first (and only?) time multiple casinos issued a coordinated set of chips, all made by Paulson with a similar look (except for the different casino names / logos) but if you compare the chips, you'll see that, while all of them are red chips with full-graphic inlays, the inserts on each of the 10 chips is different -- matching the inserts on each casinos' $5 rack chip. Rather unique!.

Shown below is one example, from the MoGH/ChipGuide website, for the Plaza. If you want to look up all of them on ChipGuide go to the following 10 downtown casinos:
Plaza, California, Las Vegas Club, Horseshoe, Fremont, El Cortez, Fitzgeralds, Four Queens, Golden Nugget, Golden Gate.