Is the regular B.Tech degree considered for working professionals ?

Are you working in shifts? If you are attending college during day time how it is possible to attend during the same hours. It indicates that without going to college, you are managing your attendance there. If your company asks you how you attended the college while you are working here what will be the answer from you. It all depends on this.
Legally you can do the part-time course while working. There are night colleges for working professionals. So if you join those colleges and study and get the degree you will not have any problem. You can't work and attend college same time. But Some private colleges are allowing students to attend examinations without attendance by collect higher fees. With these certificates, you may be able to manage without showing your experience in your CV. But in the same organisation if you submit your degree they may not honour the same.

You can join this sandwich course in Mechanical Engineering but you need to ensure the following aspects prior to joining the course. The points are as follows-
1) Ensure that there is no clashes of timing between your duty hours and attending your classes. In the event of clash, your employer may take disciplinary action against you.
2) The course being undertaken by you should have AICTE ( All India Council Of Technical Education) apart from its recognition from a recognised university from where your institution is attached. Normally such classes are run in the evening time to cover the aspirants doing their general shifts in their industries.
3) if you don't see that your course is recognised as stated above, don't join the course. It will simply kill your time.
4) The other option is take up AIME course which is at par with BE/ B.Tech course offered by the recognised university covering AICTE approval. This course was formulated by the ministry of HRD for the candidates interested for acquiring and engineering degree equivalent to degree in the engineering degree. You can clear your part wise for both the section - Part 1 and Part 2 covering 17 papers altogether. Studies can betaken up in your convenient time at your home with your ties with a reputed professional institution for better guidance. Your degree would be well recognised for both for higher studies in M.Tech or achieving a degree in Engineering equivalent to BE/ B.Tech.

If you are interested to go for a full time B.Tech in Mechanical Engineering for pursuing your career growth then there are two ways to do it. First is take permission from your organisation for attending the regular evening or morning classes. If they allow you to do so then they can give you different duty hours so that your work and educational pursuit do not interfere with each other. Second possibility is to seek long leave from your organisation for pursuing the regular course. During such leaves, employees do not get salary also and that point is to be kept in mind.
If the above does not materialise then the extreme option of leaving the present job can also be thought of though in present times that does not appear as a good solution.
The last point is that if you can somehow do this regular course in late evening without affecting your duty in the present organisation then after that if not in this organisation you can apply in other organisations for a better prospect.

Absolutely your degree will work for you. As you mentioned that you have already done a diploma course, it means that you have enough knowledge, and because of this knowledge you are part of an organization. Even during the job, you must have learned a lot of new things and it will also be useful for you. When we have a diploma or degree, naturally, the importance of a degree is found more than a diploma, so when you complete your degree, it will be given importance by your institution. Along with theoretical knowledge, practical knowledge is also very important at present and when you complete your studies with a job, that too in the same stream then you are also given priority. Still, if you have doubt that the organization will consider it or not then you can apply others.