Whaleboats were a part of the established industry of colonial Rhode Island

Omsbee's statement (discovered in 2006) is the first known mention of a whaleboat in the attacking force.  In Rhode Island, in 1772, a "whale boat" was a specific kind of boat, not likely to called a "barge" or a "longboat", both of which were larger and differently designed and equipped.  Men of Rhode Island would not be likely to call a whaleboat a longboat, or vice versa.

There was an established whaling industry in Rhode Island. The whaling ships carried whaleboats, which were launched from the ship to get near the whales and harpoon them.  Whale boats were differently designed than the longboats of a merchant vessel.  The whaleboats were light and fast and could be rowed by five men at a speed of five miles per hour.  To get the longest leverage possible, for speed, five oars were extraordinarily long oars and the men using them sat on the opposite side of the water in which their oar dipped. In other words, the oars of a whale boat run from an oarlock on one side of the boat, across the entire boat, to the rower on the opposite side (That is not a configuration of oars and rowers you would want to use if the center of the boat was to be used to carry men!) 

Whaleboats had six oars.  There were three men on each side of the whaleboat, and what we might call three oars on each side.  However, one of the oars was different. Three oars used primarily for rowing were on one side of the boat; two on the other.  On the side with two oars used primarily for rowing  there also was another oar (the sixth) controlled by the mate.   This oar was designed for steering, was a short oar, was mounted vertically, and was handled only by the mate, who sat on the same side as his oar. 

The whaling industry was sufficiently developed so that whaleboats had a common size and design.  Whale boats were usually 28 feet long and six feet wide.  The reason for the limited number of rowers was the lack of space and crew members.  The whale boat needed to also have in the boat a sail and sailing gear (it was better to use a sail to close on the whales) plus casks of line and other gear needed to harpoon and retrieve the whale.   Because the more whale boats that could be launched the more whales could be caught, and the whaling ships of the need had limited space to carry crew and house and feed the crew, the whaleboat had to be rowed by a limited number of men..  Willits D. Ansel, The Whaleboat (Mystic Seaport Museum, 1978).

Note that Ormsbee says there were only six men plus the Captain in his boat.  This fits with Ormsbee's boat being a whale boat.  The only space not criss-crossed by the oars (remember: the five rowing oars of a whale boat run from an oarlock on one side of the boat, across the entire boat, to the rower on the opposite side) was a space used by the harpooner at the bow of the boat or some space at the stern of the boat.

The accounts of John Brown's request to ship owners are uniform in stating Brown wanted the largest "longboats" available.  There were plenty of longboats available from the merchant ships that used the Providence river for a harbor.  One would not expect a whaleboat to be furnished to Brown if Brown wanted longboats.

Ormsbee and his fellow men, who left in a whaleboat, most likely came  from Warren to join the attack.