You can place a Buff beam on a Sand Viper but it does not buff it's DP (damage), only the ATK Rate is buffed. Sand Vipers should be buffed with DP by Buff beam too. The Sand Vipers are receiving the boost from Boost Aura and lavamancer Eruption correctly. The DP boost from Buff Beam also does not work if you use the Split Vipers sphere.
Steps to reproduce:
The Buff Beam also boosts the damage of the Sand Viper.