All Gorillas are different. Of the earlier Howletts males, I think only Djoum, Kijo and later his son Kifu could be fully trusted as Silverbacks by the people they knew and so those enclosures could be entered.
Gugis was untrustworthy. Bitam was goodnatured but didn't know how to moderate his play so was too strong for them. I don't know about Kouillou or Djala but they came later really. They don't enter the cages at Port Lympne a.f.a.i.k