Do lens caps fit on Marumi DHG ND filters?

I've no experience with Panasonic filter, so can't really tell if they're good or no. AFAIK those "camera manufacturers filters" are usually just rebranded filters of some known filter producer like Hoya or Marumi, quite often a bit more expensive than Hoya or Marumi proper counterpart but the "usually" above doesn't have to apply to Panasonic as well, keep that in mind.

IMHO, if the price of a Marumi Super DHG filter is fine with you, then you really can't go wrong with this filter, so I can surely recommend this one as a safe choice. if you don't want to spend that much, Hoya's standard line (multicoated, earlier known as blue series, because of its blue boxes - see: http://photo-help.com/canon/wp-content/uploads/2011/12/Hoya-52mm-Circular-Polarizing-Glass-Filter.png ) is perfectly fine - it's inexpensive, good optically, very nice mechanically and unlike the more expensive grey (HMC) and black (Super HMC) series of Hoya - it's not a horror to clean the filter.