Hello, Kmilson! Yes, it is possible to block the slimes' spawn, as I'll explain below.

Requirements: 23 or more people (better if only 3 EK)
1st step: As everyone enters the chamber, DO NOT ATTACK THE BOSS! As soon as you start attacking it, the slimes'll start spawning and it'll get harder to trap the boss
2nd step: The main EK will take the boss to the position I was on the screenshot. Usually the shooters will throw magic walls on the double mushroom line in order to make the boss pass through the right position
3rd step: After the boss gets to the position, all EK's will stand on those 3 spots marked by the brown mushrooms. If there are more than 3 EK, let the stronger ones enter on the position first so they can deal more damage. If the team has only 1 or 2 EK, make the thougher RP assume this position
4th step: After the EK's got their positioning, all the rest of the team will start getting on the spots marked by the energy bomb runes. The max range the boss can spawn a slime is 4 so it won't be able to summon.
ONLY AFTER STEP 4 THE TEAM MAY START ATTACKING THE BOSS
Bonus tips:
1 - When the vulcan above is about to explode, the team can throw a magic wall on the line of the boss in order to not cure it
2 - Even fewer members can make a decent trap. If you have 11 or more players you can trap on vertical. The slimes'll still spawn but they will be in fewer numbers, so the risk of a massive explosion is still low.
In resume:
Yes, it is possible to block the slimes from spawning in warzone 5 as long as you have a massive team (23 players+) and do the mechanics right, but if you have at least half this team (11 players +) it is still possible to semi-block the slimes so the quantity of them does not bother that much