The Nigerian Adeboyejo followed up his midweek strike in the EFL Trophy win at Oldham with a somewhat fortuitous goal against the Saddlers 10 minutes after coming on which may have finally come off Walsall defender Jack Fitzwater - but Cook hit an 89th-minute equaliser for the visitors.
Barnsley had goalkeeper Adam Davies away with Wales and midfield man Kenny Dougall with Australia so Jack Walton stepped in between the posts and Cameron McGeehan and Mike Bahre came in with Brad Potts also ruled out through injury.
Bahre made his league debut after signing on loan on deadline day from Hannover 96, having been brought through the ranks in Germany by Reds coach Daniel Stendel and having impressed in the midweek win at Oldham.
Walsall included on-loan Wolves midfield prospect Connor Ronan.
Walton made the first meaningful save when he tipped over an eight-yard header from Morgan Ferrier.
Kieffer Moore forced Liam Roberts to palm away a shot from outside the area as it skidded on the rain-lashed surface.
George Dobson almost capitalised on a slip by McGeehan but shot wide as the midfield man got back to slide in.
The Walsall captain Dobson also saw a goalbound shot strike his own man, Josh Ginnelly, and Luke Leahy hit a long-range free-kick over the bar before Barnsley almost struck in stoppage time as Ethan Pinnock headed down from Daniel Pinillos’s free-kick but Roberts pushed it aside at the foot of the post.
Barnsley brought on striker Adeboyejo for McGeehan for the second half.
The move paid dividends as the ever dangerous Mamadou Thiam chipped a quick corner kick into the path of the onrushing Alex Mowatt, who knocked the ball to the near post where Adeboyejo’s first attempt struck the goalkeeper only for the ball to rebound against the striker and trickle over the line for a 55th-minute opener.
Thiam wasted a chance when he fired over unmarked from Moore’s low cross and the towering striker also flashed a header across the face of goal as Barnsley got back on top.
Adeboyejo should have made it 2-0 in the 78th minute when Barnsley broke at speed from Walsall’s corner and Moore squared for his partner, who could only sidefoot against the chest of Roberts.
Striker Andy Cook replaced Ginnelly as the visitors sought an equaliser but it was the Reds who again broke from Walsall’s corner only for Moncur to fail to find Moore with his cross.
However, Walsall equalised when Ronan attacked down the left and moved the ball into the path of Dobson, who fed it inside for Cook to sidestep his marker and fire home right-footed in the 89th minute.
A frantic finish ensued as honours ended even, Moncur seeing a deflected shot palmed away for a corner.