Yes, Tejera will join the rotation while Burnett is on the shelf, esp. with Penny's trouble with the league.
As for his keeper value in your league, I just don't see it. He is a younger guy, but as for holds, I see Looper and Nunez getting the majority of those. I know your league is deep, but someone else will emerge on another team to provide holds.
Tejera is good for a few starts, but not worth keeping on your team after the Marlins rotation become stable.
Zack Greinke...the next Greg Maddux. LOOK IT UP!
For what it's worth.