In the following document section "Peripheral Gateway (PG)" it is mentioned in regards to the dialer that "The dialers are co-located with the agent PGs with the dialers running in a peer model."
Is there any possibility to have the dialer running on a standalone server as, co-location of the dialer on an agent PG would impact our security design with ours firewalls ?
It looks like you can put it elsewhere, if this is what you mean?
"You can deploy the SIP dialer either on a VM with just the MR-PG or on a VM with the MR PG and the Agent PG. Redundant MR-PGs and Agent PGs are required. "
This are list used to configured the outbound dialer.
Is there any possibility to have the dialer running on a standalone server as, co-location of the dialer on an agent PG would impact our security design with ours firewalls
If you're running UCCE, yes. If you're running PCCE, no.