I’ve figured it out. For the next poor soul who might come across this issue, I found this thread: boot - Including a custom ACPI DSDT with (K)Ubuntu 18.04 (RC1) - Ask Ubuntu which recommends calling acpi command directly in grub.cfg. Below works for me once I installed the acpi package in system packages
boot = {
kernelPackages = pkgs.linuxPackages_latest;
loader.efi.canTouchEfiVariables = true;
loader.grub = {
enable = true;
devices = [“nodev”];
efiSupport = true;
configurationLimit = 10;
extraConfig = ‘’
acpi /ssdt-csc3551.aml
‘’;
};
};