In my experience, having some knowledge on piano HAS made mallet playing easier to understand, maybe not to actually execute, but definitely to comprehend. In playing piano, you become accustomed the basic left hand = bass/tenor, right hand = soprano/alto set up in a 4-voice part, which is very applicable to 4-mallet playing. Also, you become more accustomed with chord structures and placements, and it makes that a little bit easier also with four mallet playing. Finally, the biggest thing, which is usually the biggest downfall for battery-based percussionists trying to attack mallets, is it makes you better at melodic reading. People have such a difficult time with reading melodic lines at a percussionist which is ignorance, in a sense, and a bit insulting, and is a big part of the reason that some musicians degrade and misunderstand percussionists.
The one thing that piano playing will not help you with is gaining an independence from staring at your keys the entire time you play. When you learn something new,
don't just memorize and regurgitate. Practice learning how to look at the music while playing around the keys, and on tough licks that are high in naturals or all accidentals, THEN look at the keyboard. I absolutely HATE it when I see a mallet player staring down at the keyboard the entire time. When you learn how to read, then you're committing melodic interpretation to long-term memory, while memorization is just a short term memory thing.
Let me give you an example.
Read the following, look away, and see if you can repeat it word for word:
"Be a percussionist, not a drummer."
See? It's not that hard to do. Memorization is low-level. If I asked you two months from now what that said, however, you probably would NOT remember. Which is why when you look at a staff and see a note that is 2 ledger lines above the staff in treble clef, you can figure out the note and say "oh, that's a C," memorize the music with the C6, and ultimately play it correctly in a performance. Then when you look at a new piece of music with that same exact note, you have to "count" your letters up again, and figure out the note and repeat the process. Learning to become a better reader is practicing more long-term memory skills, and ultimately become a better performer. Once you learn how to ride a bike and commit that to long-term memory, you'll never forget. Same goes for music. Once you learn and commit to your long-term memory where each note is located, then you'll never forget.
Piano playing is always a great thing to pick up, all in all. It will be applicable toward mallet playing in some regards, but in addition to that, it will help you a TON when and if you face music theory situations. I wish I had a drive to learn piano better when I was younger so I could use it to my advantage now in my theory class.
Anyways, sorry about the philosophical input on this, hopefully you understand what I was saying. I tried to answer your question, give you a little tip, and give you a bit more information about your question all in one.
Happy percussing!

B