No, it won't hurt.
But xp will become dependent on 98/me. If you ever have to reinstall 98/me, you'll have to do a (shudder) reinstall of xp to load the MBF again.
I prefer a 3rd party (whatever!) bootloader, so that the operating systems are self contained, and completely independent of each other. You can even make them invisible to each other, completely; as in, the OS can't even access the partition, so you never have to configure/take away the drive letter.