Yes - you'll be fine w/ no problems. Maintainers are for the battery and batteries are, for the most part, the same 'technology'. Porsche doesn't make the maintainer itself either. They usually just re-brand others. For instance, the Porsche Charge-o-mat II is just a re-branded c-Tek 3300.
Porsche
c-Tek
You can either plug it into the cig lighter (provided your cig lighter isn't switched off w/ ignition as Mike stated) or you can connect directly to the battery. Either way, what you have will work w/o any problems.