Why the port is named datadog and not datadog-agent?

What kind of failures?

not sorted

Why don't you use go:modules?

GH_ACCOUNT is not needed

Why these 2 lines are needed?

404

Why do you delete go.mod?

You can use GO_TARGET and put CGO_CFLAGS, CGO_LDFLAGS and GO_BUILDFLAGS in their own lines.
do-build is probably not needed

You can use one MKDIR only.

any reason to skip dogstatsd? for loop?

make -C ${WRKSRC}/rtloader

You can use a glob

That seems really weird as a prefix: /usr/local/bin/datadog

These variables should be defined later (after the USE_*)

It should be defined with the other USE_x