Santa's Shop Wishes It Checked Buyer Twice
Santa's Workshop, venerable Christmas theme park in Adirondack Mountains, survives brush with disaster that followed agreement by its owner, Bob Reiss, to sell park to Gregory P Cunningham Sr, who turns out to have been convicted felon with reputation as con man; Reiss decided to block sale and not open park for 2001 season, but people of Wilmington, NY, whose economy relies on park, worked to keep it open; Reiss has found a buyer more to his liking in Doug Waterbury; Cunningham is suing Reiss and insists his involvement with park was completely honest; photos (M)