Passing along a note I have, can't remember who to give credit to.
The following method was written for UGNX1 or 2, don't know if it's changed on later versions.
First save the data you want for the points to a text file with a .dat extension which is what UG reads.
You do not need to include heading information such as X Y Z to indicate which coordinates are specified in the columns.
x1 y1 z1
x2 y2 z2
x3 y3 z3
The point coordinates can be separated by a tab or space character.
To import the data points choose
1) Insert > Curve > Spline
2) choose By Poles or Through Points
3) select Points from File
4)choose your points.dat file that you saved from excel
5) Insert > Curve > Point Set
6)If you want the points to be grouped select the Group points option to turn it on.
7) choose Spline Defining Points or Spline Poles.