This website gives a little information. On the home page click on the heading Essentials, second bullet point in left hand box, then scroll down to last entry Disabled travellers.
The Hermitage's own website says this:
If you have to use a wheelchair while visiting the State Hermitage Museum you will find the following information helpful:
We recommend that you call the museum administrator on +7 (812) 710-90 -79 in advance and our staff will help organise your visit and work out an optimum route for you to get acquainted with the museum collections.
The museum can be accessed though the usual entrance from Palace square. You have to cross the Winter Palace yard and ascend the ramp leading to the doorway.
There you should ask the militia officer on duty to either open a leaf of the revolving door or call the administrator for you.
The flight of stairs leading to the entrance area is equipped with a stair lift. To put it into operation, you should ask the administrator on duty for assistance. You can find the administrator at the Information desk in the Main Vestibule.
You can obtain a complementary wheelchair from the Information desk in the Main Vestibule leaving any ID document as a guarantee.
The flight of stairs leading to one of the cloakrooms is equipped with a stair lift.
We recommend that you ask your escort to check your coat in the cloakroom for you, in order to save your time.
Ticket Check Area
Follow the signposts by the entrance to the gallery where the ticket check area is located.
The ticket check area is equipped with turnstiles. You will be able to enter the museum through a special wheelchair turnstile.
Our museum is equipped with stair lifts. They are located on the ground floor stairways.
From the Ancient Egypt hall you can access the Ancient World display only by using a stair lift. You will face the same difficulty when visiting the Treasure Gallery, the displays "The Eneolithic and Bronze Ages", "The Scythians", "Early Nomads of the Altaic Region", as well as the displays dedicated to the culture of the Caucasian peoples and the Golden Horde.
We recommend that you warn the administrator at the Information desk about your intention to visit these halls in advance.
If you are already in an exposition hall and you need to use the stair lift you should call the local extension number 1079 from the nearest telephone or use your mobile phone and dial 710-90-79.
There are two high capacity lifts operating in the museum building. The lift closest to the Main vestibule is located at the beginning of the Rastrelli Gallery. Go to the bottom of the Main Staircase and turn right into the cafe area. The lift door will be just around the corner on your right.
Using this lift you will only be able to reach the 1st floor of the museum. In the lift press button 3 which corresponds to the 1st floor level.
Should you wish to visit the displays located on the 2nd floor of the museum you should use the lift by the Commandant Staircase. Go along the Rastrelli Gallery past the shop area and keep going until you come to the staircase.
You will find the shops and cafes on the ground floor in the Rastrelli Gallery, as well as book stalls in the display area accessible to wheelchairs.
Toilet facilities with special stalls are located on the ground floor by the Main Staircase of the Winter Palace (Jordan Staircase) and by the Commandant's Staircase.
We hope that you will find your visit to the Hermitage very enjoyable!
Hope this helps you with your planning.