You might want to keep in mind that your employer has absolutely no obligation under the law to offer you any kind of paid leave in the first place. That being the case, they may legally require you to use it in any way they see fit, regardless of whether they put it into the handbook, as long as they do not violate discrimination laws.
NOTE: Requiring you to use your paid leave during your suspension does NOT violate discrimination laws unless you are prepared to show that if you were a different race, religion, national origin etc. they would not have made you use it. Unless you can point to a similarly situated employee who was suspended for a similar reason and did NOT have to use their leave AND was of a different race, religion etc. AND there is no other reasonable difference between you, it is extremely unlikely that you will be able to make that claim.
You might also keep in mind that the option to using your paid leave, is having your suspension unpaid.