I think the server, assistant server, head sevrer, and stateroom host only care about the amount of the tip, not whether the tip envelope contains cash or a tip receipt from Guest Services.
In either case, you can decide the amount you want to tip. And in either case, you present the envelope on the last evening.
Charging the tips to your onboard account (which you settle with the credit card that you have on file) is convenient and safe -- for you and for the recipient of your tip.