gold finger plating needed on prototype board edge connector?
Yes, for prototyping over short periods of time with few insertions you should be fine.  Multiple insertions will damage the coating (and worse, may eventually rub off some of the tin, leaving shavings inside the connector!), and over time vibration will reduce the contact's effectiveness.  So it's not good for long term use, but it shouldn't be a problem for prototyping, particularly if you can use a removable riser card that can be replaced in the case of damage.