As long as you have motive

As long as you have motive power on all the cars it should not be a problem. Two of my hiden stub end staging interchange tracks are on a grade of about 1.5%. You just need to notch up the engines more to get the train moving. My layout is HO.

"The grade is less than

  It's not ideal but there's no reason you can't have a sloped staging area. Just spot all the cars against an end of track bumper, or leave an engine coupled to the cut, or arrange some kind of between the track "brake" to hold the cars where you want them.....DaveB 

slight?

Some people have done staging

Some people have done staging in a helix, and the grade in helixes usually is more than 2%.

It's less than ideal to have a 1.5% grade in staging but you gotta do what you gotta do; just remember things will roll at that grade so provisions will need to be made.

If the grade slopes down FROM

If the grade slopes down FROM the main and ends in stubs with bumpers as DaveB said, that could work but uncoupling in staging might be annoying if the cars stay bunched up and roll down hill. If the grade slopes down TO the main I would think it would be highly irritating keeping cars from rolling out. Or silver linings it could add an operational twist as you need to “set the brakes” physically with some device 

Jeff

I can agree with the Several suggestions

the several suggestions made...

I might experiment with one or two more...

If you have checked the gauge of your wheelsets, you Might try altering rail gauge at the end of your staging track... perhaps adding a smear of solder on the inside of the  railhead (and shaping it with a file).

If it's to be used by a certain consist (example:  freights with a caboose), you may alter the rolling characteristics of the cabooses. 

Perhaps a pair of wide-open rail joiners is all you need.

Much of my layout has up to 3% grades... and parking on a crest, or valley, with the consist about equal on either side can overcome it rolling away.

1-1/2% is usually not enough to lose all control... subtle humps, dips, or track-laying  'deficiencies' (like imperfect track alignment = not as straight as it should be) may help you achieve what you want.

Absolutley

Why not, absolutely!

There are many examples of the 1:1 having yards on grade.  Is it ideal, nope… Is it real, yep.

People have already pointed out some good ideas if you go this route.  Just make sure you have something in place to keep trains from rolling off and hitting the floor.  

I myself have worked a few yards that have grade. One such interchange yard requires 14 hand brakes on a 100 car train to be tied on when left for interchange. It’s a sight and sound when they get a train going out of the yard. Sand flying and notch em’up!

As staging goes on grades,

As staging goes on grades, the examples I have seen AFAIK don't involve switching or re-arranging cars, coupling and uncoupling.  They have just been on-the-grade parking of trains to line them up for an operating session.  Assuming couplers are height checked and attached to an engine, a gentle grade should allow a whole train to stay put until it needs to be moved.

Staging and grade

Well, strictly said, NO... A

Well, strictly said, NO... A "staging" is not existing in the real world!

Staging is refering to a part of the layout that represent "the rest of the world" ... exactly a "stage" where "actor" stay waiting to enter the show. Usually "actors" are "trains" so loco and cars... but can be just cars depending on operations..

A Hump yard... is a yard .. to compose blocks of cars using gravity so are ready to pickup for next train.

Enzo is correct.  Staging on

Enzo is correct.  Staging on a layout does not represent a hump yard, it represents the world "off the edge" of the layout and allows trains to come from the east or west or whatever, across the region represented physically and back off.

sdpjr

A hump yard uses gravity to get cars moving; the tracks in the yard tend to form a bowl shape, so the cars don't roll out again. A hump yard also uses retarders to slow cars to a joint.

A gravity yard would be closer to this application, where the whole yard is on a slope.

Has anyone made staging in a bowl-shape? I'd imagine that would help from cars rolling onto the main or off the end of the track.