This guy seemed to have done it, and also betray his partner at the same time check this out, i'm confoozled VIDEO LINK
well, if he had actually sniped the grenade, it would have blown up. still the video was very strange.
From multiple instances, it seems that grenades are completely interactable once it appears in one's hand. I forget where, but there was a clip where one spartan threw a plasma grenade at another who was beginning to throw a frag grenade. The plasma grenade stuck to the frag grenade in the guy's hand, which subsequently landed at the plasma-thrower's feet and detonated. Also, I have pegged a grenade mid-air with a gauss hog on my own xbox, detonating it in midair (on the level "The Ark," right after the scarab first shows up). So to answer your query, I would have to say 'definitely.'
Its possible, it actually happened to me today during ranked team doubles, me and toochie were playing team sniper, she tried to sticky someone, and me at the same time tried to snipe the guy but instead shot the plasma, causing me to betray toochie and kill the guy too haha.