I've never considered using variables in the <snmp-device-notifiers> section of an alarm point probe, but it looks like it might work.
One concern is that the Notifier variable is substituting for a quoted string. I'm wondering if the quotes are making the transition, and whether it's possible to escape them with backslashes if not (substituting \" for a plain ").
The other thing you might try (and you may already have done this) is to wrap the variable name in braces, like
However, the description in the documentation, in enclosing the value of the SNMP device notifier in quotes, implies that we're looking for a literal, so I won't be surprised if variables don't work at all.
Have you tried substituting the variables only for delay/repeat/count, and leaving the Notifier as a string?