Most of the minilabs printers add some sharpening by default. However these default settings can be changed. Because of this it is impossible to know if a minilab is doing any sharpening. You may ask the lab to do no corrections and hope that they do switch off all effects including sharpening.
Fuji Frontier has two modes for prints. 1. sRGB 2. PD (stands for Printer Driver). sRGB mode convert the input files to sRGB color space and then various corrections can be added to the input files. While in PD mode , no correction is done as well as native color space is used. In this mode you can be sure that machine will not do any kind of corrections.
Sharpening is achieved by increasing contrast of adjacent pixels at a transition in an image. Any excessive sharpening will make image very unnatural. I am not sure why do you need to oversharpen for inkjet printers ?.