Blend away!
Many fragrance oils contain some essential oil anyway.
Just make sure the combined blend does not exceed the recommended usage amounts for your product.
I use lavender essential oil and vanilla cookie for my lavender vanilla blend.
Just remember, it takes far less EO than it does fo. For instatnce, in my laveneder vanilla blend I use 1/4 tsp lavender fo to 1 tablspoon vanilla fragrance oil.