For such tables, ConTeXt provides a much nicer interface. For example using natural tables, you can either use
\startsetups table:setup
\setupTABLE[align=flushleft, frame=off]
\setupTABLE[row][2][align=middle]
\stopsetups
\starttext
\startTABLE[setups={table:setup}]
\NC LongName1 \NC LongName2 \NC LongName3 \NC LongName4 \NC LongName5 \NC LongName6\NC\NR
\NC Type1 \NC Type2 \NC Type3 \NC Type4 \NC Type5 \NC Type6\NC\NR % <- center this row
\NC Item1 \NC Item2 \NC Item3 \NC Item4 \NC Item5 \NC Item6\NC\NR
\NC Item7 \NC Item8 \NC Item9 \NC Item10 \NC Item11 \NC Item12\NC\NR
\stopTABLE
\stoptext
or if you are not sure where row you want to center-align upfront, use
\starttext
\startTEXpage[offset=3mm]
\bTABLE[align=flushleft, frame=off]
\bTR
\bTD LongName1 \eTD \bTD LongName2 \eTD \bTD LongName3 \eTD \bTD LongName4 \eTD \bTD LongName5 \eTD \bTD LongName6\eTD
\eTR
\bTR[align=middle]
\bTD Type1 \eTD \bTD Type2 \eTD \bTD Type3 \eTD \bTD Type4 \eTD \bTD Type5 \eTD \bTD Type6\eTD
\eTR
\bTR
\bTD Item1 \eTD \bTD Item2 \eTD \bTD Item3 \eTD \bTD Item4 \eTD \bTD Item5 \eTD \bTD Item6\eTD
\eTR
\bTR
\bTD Item7 \eTD \bTD Item8 \eTD \bTD Item9 \eTD \bTD Item10 \eTD \bTD Item11 \eTD \bTD Item12\eTD
\eTR
\eTABLE
\stopTEXpage
\stoptext
both of these give

\rowstylethat takes the cell contents as an argument – Werner Feb 21 '13 at 19:35