The first two years he had OPS+ of 101, which is decent, and then 112 which is pretty good.
Then he was 88, which is subpar, and this year 29 which is terrible.
Lifetime it's 93, below average, 100 is league average theoretically.
In addition, his walk/strikeout ratio is quite poor and his power isn't special, except for one year when he did hit 18 homers.
If this is the player you want in CF, based on some career norm, go for it. Not I. Although it might be worth it to play him some on the theory that he can't possibly be as bad as he was earlier this season.
As for defense, I have no problem with Heisey playing some CF, but obviously you have to look at both sides since he has to take his turn at bat.