I agree with Tim. Their workflow is probably designed to input sRGB because the bulk of their work is from people who have simple cameras and do no post-processing. The WF will include the conversion to the space for their printer and you will probably have a double conversion if you do one at home. The exception to this rule is the top--end print labs whose WF includes a profile aware step and who will therefore properly handle any image in any space. I don't know which category Adorama fits into, but I suspect it is the former because they are a high volume and low priced lab.
Soft-proofing is merely a tool for your convenience in order predict what the print will be like. In ordinary viewing (not proofing), if your color management is set up correctly the same image in different spaces (ProPhoto, Adobe. sRGB or the printer space) should look the same on your monitor. This is the essence of CM; the application reads the profile and then alters the display data to fit your monitor profile. This is only done to the data sent to the monitor, not the original image data, but no matter what the starting point (the embedded image profile) the display should be more or less the same. When you print at home the application does the same thing but this time to the data sent to the printer, converting it to the printer's space. If you print from a non-CM application or elect to not have the application handle the conversion, the printer driver does the conversion. In eitrher case you do not do a permanent conversion of the embedded space.
When things are uncertain, always have the lab do some softproofing of several shots at a manageable size to judge how compatible they are with your setup.
That would be "hardproofing".