Apart from August, March has the second highest level of precipitation in Svalbard. Although this is not much in comparison to other countries (29mm/month) the rain/snow in Svalbard comes in constant light drizzle so it is probable you will get wet during your trip if you choose to visit in March.
When there is light during this month it is likely to be interesting for photographers, especially as you have both sunrise and sunset in a short space of time. This means you get both golden hours in your waking day (a novelty for Svalbard) and with cloudy skylines you could get some great images.
Snowmobile safaris can run from as early as February in Svalbard so March can be a great time to explore.