According to The Complete Peerage, 2nd edition, volume 1, page 87, George Monck (supposedly half-brother of William Womack) was the second son of Sir Thomas Monck, of Potheridge, Devon, and Elizabeth, daughter of Sir George Smythe, of Madford in Heavitree, Devon and was born at Potheridge 6 December 1608.
There is no mention of any connection to the Womack family, and given George Monck was born in 1608 and William Womack in about 1575, it seems to be a long span of years for them to have the same mother (though not impossible).