I'd be inclined to trust the mfg's advice, but protect the pins with 74S1053 clamps or discrete Schottky diodes clamping the signals to Vcc and Gnd. If neither end is using an out-of-tolerable-range supply, there shouldn't be much risk, and, as for stray signal, well, the diodes at either end will minimize that. If LVCMOS can drive the 8 feet of cable, so, too, can the MCU. Moreover, the diodes in the MCU will probably protect the part, too, but you can be conservative if you like. Now, if the cable were longer than 7 meters ... well, that would be different, though I'd still want the clamps, driver or no.

I guess a lot depends on how your costs work out. IIRC, a small, 4-diode Schottky diode array would cost very little, though.

RE