surely the easiest way would be to ask at reception before booking

No they are not connected by a footbridge, or they werenot a couple of weeks ago

Whether or not connected by a footbridge, most motorway services are connected by a vehicle underpass. Use of these underpasses is usually restricted to staff, delivery vehicles or emergency services, but there may be exceptions where the public can have access if there is a need to use a service (such as a pre-booked hotel) which is located entirely on one side of the motorway. It would be worth enquiring with the hotel to verify what access facilities are available.

David
EDIT: a service road is mentioned in the 'Directions' section of THIS website, but it would still be worth verifying with the hotel unless anyone else can confirm from previous experience.

Hi there there is a service road then you have to go round country lanes for 2 miles to get to the service lane the other side-and there are barriers so you need a pass key to open them!
The Burnham-on -sea junction is 2 miles further on so you can do a U-turn and come back to the services on the Northbound carriagway!
trouble is youll have to travel 7 miles back north to do a U-Turn at
weston-s-mare, although the service road northbound is nearly always open!
your best bet is to stay at the Premier Lodge in Weston-s-Mare just 2 miles off the junction