Will they continue to send up new buds throughout the summer, or will it not make any difference at all if I remove them after they blossom? I have at least six very tall leafy plants, but not many buds.
There is conflicting information on this subject - to some extent, it depends on which Hibiscus, that is, whether they're hardy like Hibiscus syriacus, which starts flowering around July on into early autumn, or the more tropical varieties which flower most of the summer. Some sources say not to deadhead, that it discourages further flowering, and others say the opposite, examples of which are shown in the links below
Not knowing which varieties you have, its difficult to make a recommendation, but if they're the tropical type, I'd be inclined to experiment - deadhead half the plants and leave the other half to see if there's any difference in subsequent flowering. In the UK, we tend only to grow Hibiscus syriacus - some people don't like seeing dead flowerheads and take them off, other people don't worry about it and let the plant do its own thing. Doesn't seem to make much difference either way, except a deadheaded plant might look a bit tidier.
Having much experience with both the short answer is yes. The plant lives a fuller more healthy life when properly groomed. The removal of spent blooms benefits the health of the plant. The Hibiscus will continue blooming if spent flowers are not removed but you leave you plant susceptible to destructive insects and mold when it is not properly cared for.
Note section specifically addressing the removal of spent flowers.