Shane,
Translation rules are not always necessary in an SRST environment. It really depends on multiple factor include, the type of connection to the PSTN (ISDN, FXO, SIP), the dial-plan for the IP phones and the differences in inbound call handling when in CUCM vs. SRST mode.
Translation rules are more important for inbound calls. Especially if, within CUCM, translation patterns are in use. For inbound calls, translation rules are useful for redirecting calls from their original destination, which may not be available in SRST mode (think Unity, UCCX, Unity connection) to an IP phone of a receptionist so that the call can be handled. For outbound calls, translation rules are typically used to modify the calling party number as the called party number can easily be modified using the configuration under the dial-peer, to strip or prepend digits.
If outbound calls are failing in SRST mode, then I would first check to see that the dial-peers are configured to route the call out the correct interface before suspecting translation rules. For inbound calls, especially if the called party information does not match the extensions on the phones, I would suspect a translation rules issue.
Below is some additional documentation on this topic.
http://www.cisco.com/en/US/customer/tech/tk652/tk90/technologies_tech_note09186a0080325e8e.shtml
Hope that helps.
-Felipe
