Maneuvers can't be initiated when in the viper form granted by that cape
The cape of the viper (Magic Item Compendium 84) (2,000 gp; 1 lb.), in part, says
While in viper form, you replace all your normal statistics and special abilities with those of a typical viper of the appropriate size, except for your alignment, your hit points, your Hit Dice (for the purpose of adjudicating effects based on HD), and your ability to understand (but not speak) the languages you normally understand.
(Emphases and link mine.) As the emphasized text indicates, the loss of special abilities includes the loss of extraordinary abilities, and Tome of Battle on Martial Powers and Magic says, "Unless the description of the specific maneuver or stance says otherwise, treat it as an extraordinary ability" (40). This means that in Tiny viper form your martial adept can't initiate the maneuver death from above—or any other maneuvers—unless the DM rules otherwise because it would be hilarious.
Note: The adept's speed is that of a Tiny viper when in Tiny viper form as the adept's normal speed statistic is replaced by the Tiny viper's speed statistic. Further, if the DM rules that statistics include the adept's creature type (and, to be clear, this DM would), the adept's current animal creature type grants the adept proficiency with the Tiny viper's natural weapons; however, if the DM rules that the half-orc adept retains its humanoid creature type in Tiny viper form, then in Tiny viper form the half-orc won't be proficient with its newly acquired natural weapons… and that's a little weird.
