A group wants to maximise the potential for surprise attacks using their stealthy members. They don't want their less stealthy members to blow a surprise attack.
A party of four; two stealthy, two not. The two stealthy members travel in to a room (~30 feet or so) and leave the two non-stealthy members behind the door/in the previous room (hidden).
The two stealthy members throw to surprise some monsters in the room. After the first round of combat (which may include the monsters being surprised and not acting), the second round of combat starts and the two non-stealthy adventurers enter the room and enter combat. The two non-stealthy members did not want to try and surprise the monsters, they know they're too noisy, so they wait outside the room and out of sight and still.
The party is two rogues with +7 Dexterity (stealth) and two dwarfs with -5 Dexterity (stealth). The dwarfs don't want to blow the potential to surprise the two orks with passive Wisdom (Perception) 15, they want to stay out of the room containing the two orks.
The two rogues throw stealth checks of >15 and the orks are surprised. The first round of combat occurs (containing only the two rogues and the two orks), the orks are surprised and cannot attack. After the first round of combat, the orks are not surprised. The two dwarfs now run in to combat, with initiative being throw for this 6 creature group.
Is this permissible under the rules? Would DMs out there ask for/permit this selective throwing for surprise and (after that) for the rear guard to enter combat after the first round of combat (in which the monsters were surprised)?
This is related but disimilar from How to determine surprise when only part of a side is stealthy?. I am asking about the temporary splitting of a party to allow a stealth member only surprise attack followed by non-stealthy members entering room and entering combat.