I would say it may not be safe to delete a MBR but it is safe to let another or the same boot loader overwriting it.
Reason : The MBR has the partition table embedded in the last 66 bytes (4 partitions each 16 bytes + 2 spare bytes). Unless one knows how to delete the correct portion of the MBR the accidental removal of the partition table can render the disk unusable, at least temporarily. I have not come across any standard command to delete the MBR too.
Observed practice : Every PC boot loader can restore its MBR and always keeps the partition table intact. Thus it is safe to let one MBR overwrite the other using the system's own command.
Finally the MBR, less the partition table, is replaceable. It is the interior of the partitions that is of value and should be protected and should have a back-up. The MBR is the first sector of the hard disk and is only 512 byte large. If a user keeps a copy of the partition table then the entire MBR is dispensible. The destruction of the partition table only destroys 64 bytes but the partitions' interior is not touched. Therefore the MBR can be retored and the partition table can be rebuilt without any consequence. Done this a lot of times.
It is common for an operating system to reject a hard disk if it cannot cope with the error in the partition table. If an operating system reads a hard disk then unofficially it implies that the integrity of the data can be guaranteed. Most OS opt for not touching it than trying to solve the problem.
Linux is superior in handling hard disks because of its rich set of Bash commands. When other systems cannot cope with a hard disk with big problem in the partition table "cfdisk" could normally still be able to read it. If all others fail then Linux's last line of defence is "fdisk" . From my experience while all others refusing to touch a dodgy disk Linux's fdisk will still handle the disk, reports the problem and most importantly can be use to delete the dodgy partitions and to bring back a healthy disk again.
If Linux's fdisk refuse to read the disk then in my experience that disk is likely to have a mechanical/hardware problem and on its last leg to a junk yard.
Try this command when everything fails
If you see an output then fdisk is usable for changing the partition table.
To rescue a hard disk with an accidentally delected or partially deleted a partition table use "testdisk"