Yes, you will need to use an isolator. The line from the isolator to the fuel press guage needs to be filled with a liquid that is compatible with the guage and the diaphram in the isolator. Usually it is 50/50 antifreze, but some manufacturer may have other recomendations. Also, I would sugest braided. If you use a rubber hoser, it can expand and throw off the reading on your pressure guage.
Also, electric is much easier to set up, you can route the wires wherever, unlike a mechanical temp where you have a set length of thermocouple line that has to be coiled up somewhere. For the oil press, electric is good also. if a wire breaks, you lose reading. If the 1/8" pressure line to the guage gets brittle and cracks, you then have an oil leak that you may not notice untill all the oil has drained out of the crack, or if it breaks inside, you then have an oil slick under your dash.
my .02
http://www.jegs.com/webapp/wcs/stores/servlet/CategoryDisplay?lang=-1&catalogId=10002&storeId=10001&categoryId=23065
The isolator I have.