Well, I originally imagined it was some kind of valet service (i.e. to do with grooming); however, most of the FR sites I found (i.e. not ones translated from another language) seemed to refer to 'someone to carry your shopping from your car...' — which I suppose does really tie in better with the original idea of a groom: someone who would take care of your horse when you arrived.

So really and truly, it looks as though 'porter' is closest; I did wonder about 'footman', but I'm a little sceptical about that used in any kind of contemporary context...

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Note added at 2 hrs (2013-09-28 19:18:54 GMT)
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So although we talk of 'valet parking' (this is included in the bell-boy job description from some sources), in an hotel we would indeed talk of a bell-boy (or bellhop); however, I'm not quite sure how well this works in a purely conference situation (i.e. if there is no actual accommodation involved). So I stand by the possibility of 'porter', which can probably safely be applied even in the most general of situations (and notice that hotels have porters too!) I have a sneaking suspicion that bell-boy / bellhop is possibly more US (I have always heard it in US films, and many of the Google results I found did indeed come from US hotels or chains), while 'porter' is possibly more UK...