SNAT and NAT on difference vlans

What if some of the source servers need a 1:1 snat?

i think using snat instead of nat is easier to control because, you want, some client has multiple ip (e.g. one nat and one snat). since you are going to use snat for 1-to-1, you also need to create another virtual server to accept traffic initiated from external (inbound traffic).

Does this have to become one giant monolithic irule, where every case specific case is handled in an elseif clause? Or would you then create more source-specific virtual servers for anything that needed a 1:1 SNAT on any of the interfaces?

each has pro and cons. if i were you, i would pick the one i feel comfortable in maintaining it. :)