Okay, that explains a lot! When I first read this thread, I was more under the impression that you wanted to insert a prop model in HL1 (such as, let us say, a car). Inserting the actual models is very easy, making use of an ambient generic. (Or in the case of not living props: monster_furniture.) The problem is though, that this doesn't copy the AI the monsters have. For this, you'll have to copy the Azure Sheep dll files into your mod and, equally as important, put these monsters in your map using the Azure Sheep fgd file!
I don't know if Azure Sheep came with such files so you'll have to look for those yourself. My guess is that the fgd file wasn't made publically available and thus if you want to include the Azure Sheep models and their AI, you'll need to ask those files from the Azure Sheep team. (That, and of course their permission to use their material, as its copyrighted.)
Another problem is that, even if you get the Azure Sheep code, then you also want to include the Genome monster. This is conflicting as you can only use one dll file. What you'll have to do is, somehow, obtain the source code for both mods and then implement that into one dll file and one fgd file. So yeah, there'll be quite a bit of coding involved.
And implementing the models should just work if they're in the riht directory. Just make sure that when your map is in your modfolder (for instance: sierra/half-life/silentdeath/maps/) and in the map you've got the model from this path: sierra/half-life/valve/models/ then it won't work. This is because it'll then look for a folder called sierra in your silentdeath directory. The solution is to place the models from the valve models folder into your silentdeath model folder and refer to the model as models/modelname.mdl in your map. Of course, they'll still stand still, going through idle animations, as they still have no AI.