yes. no matter the case, they should be allowed to enter a survival show. there's a whole bunch of different cases one could talk about, and in all of them i don't see why they shouldn't be allowed. even though hui's appearance on boys planet sparked some controversy and i myself am not sure entering a survival show forming a group with a 2.5 year exclusive contract was necessarily the best call to take... who am i to judge? he did it for his career, and it ultimately did end up bringing some attention to him and his group. besides, cube isn't doing shit for pentagon, sure they just dropped a jpn mini but idk it feels like very little noise was made? in late 2022 we had eunbi on a variety show w her bestie shinwon mentioning that pentagon were preparing for a comeback. what happened to that? we have yuqi saying that wooseok's computer is full of songs he's written and they're all very very good. what happened to that?
though ofc there's a number of cases. hui's case was slightly unique ngl (solidly mid-tier idol with decent public recognition joins survival show forming group with exclusive contract), the main difference between him and say nu'est/kaeun/yujin is that pentagon weren't almost completely dead by then (and that if we consider non-rigged votes, minhyun, baekho, kaeun, and yujin all made their respective groups... sure we don't know who was actually rigged into w1 instead of baekho but i really don't think it was minhyun).
you also have different cases. nugu rookie group members entering shows forming groups with exclusive contracts (think nine.i, also another example i can think of is dia but pd101s1 was none-exclusive) can bring the group some attention. then you have non-idol focused survival shows. jinho entered phantom singer 4 around the same time as hui on bopeul, and received nothing but overwhelming support, and even made the finals. other cases (though not necessarily as successful) would be chaeyeon's stint on swf, and ofc the whole concept of be mbtious - an idol's road to smf.
then you have very special cases: shows made for active idols but putting a spin on it. the most direct case i guess would be queendom puzzle - while i have concerns about it overworking the rookie idol members of el7z up, it's a great career boost to members like kei, yeeun (those who left their agencies), and yeoreum (sure she's still in starship but wjsn have slowed down, everyone's focusing on individual gigs). but then like there's also girls re:verse,, creating a vtuber group made of idols - active and non-active. i see.
all in all i think no matter the case an idol should be allowed to compete in any type of survival show. it's the climate of the industry they work in, something like this can boost their careers