Correct. This is what the API offers. You need broadcaster permission from the broadcaster to check subscriber status via the API.
Since you said “API” this is what I thought you were after.
Well the emote only “works” and has emote placement in the IRC message tags if they are subscribed to the channel that emotes belongs to.
Like if I use a lirk emote it’ll just show up as plain text with no placement rules, because I’m not a lirik sub.
But if I use a cohh emote it shows up with the image and the placement rules.
For example
@badge-info=;badges=broadcaster/1,twitchconAmsterdam2020/1;client-nonce=264ef2a063a62b6538719559afee8fe9;color=#033700;display-name=BarryCarlyon;emotes=74353:8-13;flags=;id=2e53c5f3-8fd5-47dc-b759-ba6878ba08da;mod=0;room-id=15185913;subscriber=0;tmi-sent-ts=1594594886854;turbo=0;user-id=15185913;user-type= :barrycarlyon!barrycarlyon@barrycarlyon.tmi.twitch.tv PRIVMSG #barrycarlyon :lirikBB cohhHi

You’ll see in emotes of the tags it only has placement rules for the cohhEmote in the message, but not lirikEmote because I’m not a lirik sub.