Are road caliper brakes usually compatible with any model of lever/STI shifter?
Pretty much right -- you just have to make sure that the calipers have enough reach to brake (on an Allez, pretty much anything but a long reach caliper will work). There are some threads like this with some new Shimano stuff (new Super SLR) which is technically a ymmv/you're on your own, but it should work. 

Another thing you should check when replacing the brake is that the cabling was done properly -- bad brake cable routing, for example, can make your brakes not feel good.