To answer the original question, I'd say you absolutely need a HP filter.
I recently destroyed a Beyma 15P1200Nd during testing, as the software was running the sweeps an octave past what I asked it to do (turns out its in the manual, who knew?). Set for 30Hz-100Hz sweep. Cabinet is a 1/4-wave transmission line that tunes to the mid-30s. Push the levels up for a high-power sweep and bam, 500w+ of 15Hz sine. The driver is rated for (and manages) 52mm p/p travel before damage, which was very impressive to watch. The cone got itself some fold lines and had to be reconed, to the tune of over £100.
Sure, the phase will go wonky at the bottom of the passband, adding a little group delay (the audibility of which is contested). Better than your bass going to mush because the kick drum port puts out a poof of air at infrasonic frequencies and you haven't set a simple filter. Or maybe someone will drop a mic. Whatever. Its not worth the risk.