if viz is any thing to go by then Apoo betraying Kidd seems unlikely. Who is the " our" mentioned by Apoo that was in contact with Jack. i mean people say this silly thing that The black cat of hawkins had a role to play in the ease and frequency of the beasts pirates finding zou. when it was stated by Kinemon they were chased, which could have explained the first time visit, leaving only the second and current visitation as likely but ignore the obvious, Kidd alliance has outlined their goal: Shanks. On every forum i have browsed nothing has been said or speculated on the possible reason apoo and possibly their alliance was conversing with Jack, Jack also went for the easier route of eliminating zou instead of going up and see what he finds. inspite of mentioning the possibility of the minks recovering,correctly, could he have been pressed with time with what ever Apoo and co is currently cooking up?
Plot stopped both Zou's death and Any premature battle with Jack while at the same time kickstarting the war with the yonko. Luffy words to momonosuke can be seen as that as well as his eventual visit to Whole cake.
so, Kidd et al wants Shanks head, Kaido wants the biggest war ever, if Pekoms wording on the power of the yonko is any indicator, then imprinsoning kidd will not be for information. If Kidd's scars and attitude says anything is Dying is more acceptable than bowing and begging for life, if kidd chose to fight till death im betting my dollar killer and his crew would follow suit. thing is neigher kaido or any of the Worst generation would die in that manner or timing.
If those 4, at Kidd base were going to bow in subordination they would have in the two years. But despite kidd outlook he with his peers who I am sure he sees as his inferiors were able to join up in arms, or with Luffy and law two years ago why would he dismiiss the possibility of using a yonko as part of his alliance arsenal to add to the resources he spoke of. Sure Kaido is powerful, so is every yonko, as Apoo confirms they have no problems with allying with significantly weaker crews and groups.
So as important as kidd might be, the chances of him being imprisoned for over a week or so, for what? look how important Oden was and with his failure to comply was boiled alive, so not only is it impractical and meaningless as far as what we know to have Kidd imprisoned on Wano, but would torture and the beast pirates patience really be that long lasting. (Althou we know not what became of caribou, but even then Kaido untill news broke of joker and after his meeting with Kidd et al would he meet the so called leader of insurgence)
so with what was told about Kaido's patience would he really sit around lookimg at a subjugated Kidd? which is why im going to speculate that those legs are Kaido's until proven wrong as nothin which was stated by fellow Op fanatics were imo convincing that Kidd is locked up, and Apoo betrayed them.
Although I don't see the Kidd alliance actively opposing luffy and law, afterall, they were the only people who for all the word certains denotes seemed sure Kaido is the target and rightfully so, i really want to believe they are using kaido's arsenal to accomplish their goal while they will try to not compromise their rivals directly. Unless of course They with the intel of yonko Kaido plans on using luffy as bait.