Both were in the Springboks side which crushed England in the 2019 World Cup final in Japan.
De Allende and Snyman are said to have suffered "more substantial burns" to their legs, hands and face. Haley and Stander, who suffered hand burns, are expected back at Munster training this week.
Munster coach Johann van Graan said: "We are hugely relieved that the lads are all okay.
"The players have all been treated and are being well looked after with Damian and RG meeting the specialist again later this week to review next steps of their recovery."
SARugbyMag reported "both are still expected to link up with the Springbok squad".
Snyman was already sidelined, recovering from a knee injury. The four-test series between the Springboks and Lions begins in mid-July.